Kris Avonts

Hello, When using a scanned ship plan as a background image in a CAD program, it often shows some misalignment or even distortion. That makes it more complex to build a precise model out of it. I usually try to fix things with an image manipulation program (e.g. Photoshop, GIMP, …) using several transformations: rotation, scaling, shearing, … and even perspective corrections. That goes a long way to reach a perfect aligned plan but it is also time consuming and difficult to get it pixel perfect. So I made a little python program that can do a pixel perfect perspective transformation based on set of reference points that you define in the image you want to adjust. Let me show my first attempt with a simple test image. Imagine that this is a sheer plan with a base line at the top of a keel and a fore and aft perpendicular. The base line is not horizontal and both perpendiculars differ from a vertical with some (different) slant. After transforming it with my program it looks much better. The base line is now horizontal and both perpendiculars are vertical. The whole image is remapped using a transformation matrix calculated from the set of given reference points. That is why the edges now show misalignment and slant. The empty pixels at the edges (black) could be corrected by filling the pixels that fall outside the transformation with the background colour (white in this case). At this moment the reference points are hard coded into the program and the test image is also ridiculously small. So it will be of no use to anybody else but I will work and test a bit further until it is more user friendly and then I can upload it here for interested ship plan users. Best regards, Kris

Hi Tony, Glad to see that you made such nice progress on your schooner. Sorry I didn't post some updates of my efforts to create a hull for a 74-gun ship. But last week I finally succeeded in making several surfaces that represent the hull quite well. Only at the stern it still has some 'wrinkles'. Maybe it is good enough to start lofting timbers. Here is the framework of stations, waterlines and other guiding lines made from sketches. And next you can see what the hull looks like based on the above frame. So, after all, it is possible to make a ship hull in FreeCAD.... ...but it requires significant effort and patience before a result shows up. I hope you succeed in all your detail work with the schooner. It is inspiring. best regards, Kris

Hi Kiyoo, This looks a nice and elegant way of creating the required lines for frame timbers. I'm however quite surprised regarding your effort estimation as you have given in reply to Druxey's question. If I look at my own efforts, I would rather spend months instead of days to reach that state. Well done! May we also get a clue about the specific drawing software (both 2D and 3D) that you are using? I'm a fan of FreeCAD, mostly because it is 'free' in every sense. best regards, Kris

For me, it looks like a smart variation on the impossible dovetail joint. Anyway, it is fine craftsmanship. best regards, Kris

Hello ASlrWnt2C, As a first indication you can take a look at this picture which is part of plate IX in William Falconer's dictionary. The middle gun shown is run in as far its breeching lines allow. Maybe that can help you further. best regards, Kris

Now let’s go for the last mile of this thickness sander. The drum or roller is massive beech and has only 2 centred holes of 6 mm at its ends. So it must be supported from both sides by a 6 mm steel axle. I mount these 2 axles with a flanged bushing in the MDF side plates. The 2 holes (26 mm diameter) for the bushings are drilled in one go on the drill stand with the side plates aligned. Each bushing holds 2 bearings so that there is almost no play on the 2 axles. The next picture shows the side where the drive of the drum is done, shown from out- and inside. The other side has just a free running axles, shown next from in- and outside. I changed the flange such that I can easily take it out without needing tools. It comes in handy when you want to change the sanding drum. Now that the drums can be driven, I took some time to sand the wooden drums so that they are parallel to the height table and have almost no eccentricity. A thin flat metal plate with some sanding paper mounted with double coated tape was used. Patience and regular checks of the eccentricity with the motor turned at low speed resulted in a nice set of sanding drums. A dust extraction is the only thing yet to add. It is made with 3 pieces of MDF that will cover the top of the sanding drum. The sides are covered with segments cut from a plexiglass pipe (50 mm outer diameter, 3 mm thick). You can see that I use the 3 MDF pieces to transform the round hole into a slit that covers almost the total roller width. The plexiglass tube segments got small tabs crewed on to have some grip for placing or removing. The bottom of the large MDF piece has 2 grooves (2 mm deep) where it will meet the plexi segments. I added 4 small pieces of beech that are glued in these grooves and then got a round-up with a chisel. They should hold the plexi segments in place and provide some ‘click’ when mounting. Here the top part is mounted. And next is shown how the plexi segments are added. They just sit on tiny nylon tube parts sticking out about 3 mm from the side plates. Once supported the plexi segment is rotated up until it click’s against the MDF part. I almost forget to mention the drive of the DC motor. Its a 15V 10A power supply with a PMW (Pulse-Width Modulation) circuit added that feeds the motor. Now the thickness sander tool is ready for use. It is shown on my workbench with the dust extraction attached to the vacuum system. And to complete the circle I add a size comparison of old and new sander. This ends my story on the new DIY thickness sander. I hope that you enjoyed it and maybe it can inspire you for some more tooling projects. Best regards, Kris

On we go with finishing the height control in this part. The bevel gearbox I used was bought at Conrad and they have the next data sheet on their website. datablad-222355-mfa.pdf As you can see in the picture it has some annoying bolts and nuts that stick out from its body. I remedied that by drilling counterbored holes at both sides of its body. The screw heads just fit in and the nuts are melted in with a soldering iron. After mounting all bolts again, the sticking out parts are ground off. Then it was easy to mount it on top of the gearbox with 2 pieces of MDF (see last picture in the previous part). The axis is now horizontal but has to be lengthened to bring it to the outside of the tool. The next picture shows all the parts to do that. The steel rod is 8 mm in diameter and will be supported by 2 bearings sitting in a flanged bushing, shown next (different axis in this image). I have several of these and I will also use them to hold and drive the sanding drum. I only need a 26 mm diameter hole in the MDF side plate. Next it is shown already mounted. Then mounting all the pieces can start. First the connection with the outgoing axis of the bevel gearbox is made. Then an axle lock is placed (not yet present in the next picture). Then we continue from the outside again with an axle lock, a nylon washer, a rubber O-ring, the self-made dial and a 2nd O-ring. And we finish with a nylon washer and a 60 mm diameter handwheel. Done! Then it is time to add the height table and verify how turning the whole construction feels. In the above picture the bearings on top of the spindles have yet to be mounted. Once that was done the table can be moved up and down with the handwheel. To be honest, you cannot turn it with just 1 finger, but with some firmer grip it is OK. I use the handle only for large movements of the table, smaller advancements are done with grip on the wheel. With the table in its upper position you can reach the nuts that support the table through the some extra 26 mm diameter holes in the side plates. Now the table can be levelled. With a straight metal piece as reference (a square in my case) and some light from behind, that was easily done. Tightening the locking bolts finishes the height table construction. As some distraction I can also show how the dial was made (I hope ’dial’ this is the correct word to describe the ring with the scale on it). First some ½ hour sawing the aluminium base material. Then the same trick with the poor-man’s divider, this time with a gear having 45 teeth, and the proxxon drill to make grooves for better grip. Then turning the ring around in the lathe and making the scale (again using the gear with 20 teeth). Some improvisation was needed to mount the chisel. A simple tool holder with very sharp chisel mounted on another one that has height adjustment and a 2.5 mm diameter drill between the 2 to get some slant. The scale is printed (in reverse) on a transparency sheet and wrapped around the ring. It is fixed to the ring with some tape over it. That’s it for today, see you next time to finish with the sanding drum mounting and adding the dust extraction. Best regards Kris

Hello Bob, Yes I can access that article. It's of a more classic design but well adapted to the lathe. Certainly enough power to sand wider pieces of material. The popular mechanics article, I also discovered that some time ago. It is still inspiring for its straightforward and simple construction. thanks, Kris

Hi Jaager, the 4 degrees of freedom actually reduce into just 1 degree of freedom by the gearbox construction. That will be shown more clearly later. Let’s go on because it still doesn’t look like its going to be a thickness sander. Adding the side plates (also in 12 mm MDF) will help to imagine what the final tool will look like. Here is a model that shows both side plates. The plates are asymmetric because I wanted to integrate the motor in the left plate. The motor is a brushed DC motor of the ‘pancake’ type. It is shown next. While small it is quite powerful when run at full speed. To mount it a large hole was made and then a recess to accept the flange and bring the motor pulley to the plane where the larger drum pulley will come. The hole and the recess are made with an adjustable circle hole cutter and then the recess was cleaned up with a chisel clamped in some support to get the correct depth. Then it was time for a test drive. Now we switch to the height table. That is also a 12 mm MDF plate that will sit on the 4 spindle nuts. Because The part of the nut that fits into holes of the MDF plate has 10.2 mm diameter and since I have only a 10 mm drill, the nut was turned down to 10 mm on the lathe. A piece of scrap MDF was used to judge the fit: firm but possible to rotate as is required for levelling the height table. To get more grip on these nuts for adjusting, I made some profile on the outer edge. That was done on the lathe with the main spindle turned into a simple self-made divider and my proxxon drill with 3 mm mill mounted in the tool holder. The parts to make the setup are shown next. The tread is M5, the gray parts are cut from hammer nail plugs, the gear has 20 teeth and the hex key is an ‘Ikea’ key ground down at the end to fit in the teeth and in the middle to fit into the groove on top of the lathe main spindle block. All pieces mounted and in use is shown in the next picture. The height table seen from the bottom side. You can see that I added a small clamp to each nut to prevent any movement in Z-direction. And an image from the side where you can see small metal plates worked in that have a fixing screw in the middle for securing the adjustments made when levelling the table. As a last addition we have to thicken the height table so that we can use it for a sanding thickness range that goes to 0 mm. A 3mm spacer plate (hardboard) was glued on the height base plate and then an extra 12 mm MDF plate was added and held in position with 2 metal pins of 3 mm diameter. This extra plate can always be removed if you want to sand very thick pieces. Now we can move on with the construction. The gearbox with its top plate mounted is attached between the 2 side plates. You can also see a miniature bevel gearbox (90°, 1:1), the black part, that sits on top of the gearbox and brings the height control to the side of the tool. Details about that construction come in a next part. Best regards, Kris

Jaager, this is going to be a 'mini' sander. But I will take care with the wood flour and provide an adequate dust extraction solution. In this part I will show how the basic construction is made. The idea is to have the height table mounted on 4 spindles. Turning the spindles will move the table up or down. This can only work if all 4 spindles have synchronized movement and depend on just 1 height control. As spindles I chose to use a lead screw type known as TR8x1. This has trapezoidal thread with 1 mm pitch. I ordered 4 screw/nut combinations of 200 mm in China (12.59 euro). The next picture shows the spindles and some dimensional data. To have these 4 rotate simultaneously, I interconnect them with gears. So I make a kind of gearbox that will be sandwiched between 2 bottom plates of 12 mm thick MDF. The next picture shows a model of the gear configuration. All gears have 1.25 as module, the large one has 48 teeth and the small one has 32. So measured from centre to centre we have 0.5 * ((48 * 1.25) + (32 * 1.25)) = 50 mm. The next image shows all dimensions. The spindles stand 141 mm apart and that is enough width for my height table to move between them. The next series of pictures shows the build-up of the gearbox. To start we need 2 plates of MDF that are of exact same dimension (170 x 220 mm), so I saw them together on my little table saw. Then we need a lot of holes at very precise positions. I made a simple jig with 3 holes of 3 mm in line and at exactly 49.9 mm between centres. Why not the nominal distance of 50 mm? Well, I wanted to eliminate the play between the gears. It was not a total success because when you reduce the play, other artefacts like eccentricity will come into play more dominantly. The 2 MDF plates are fixed to one another with 2 screws in opposite corners. The the first hole was made in the middle. From then on I used a 3mm steel pin in the jig to position the plates at the correct centre distance for a next hole. I made 14 holes in total. Then the 2 plates are separated and 10 holes needed to be widened to a suitable dimension to fit a flanged bearing (12 mm) or a steel rod (8 mm). This was done by first mounting a 3 mm drill bit in the drill stand to bring the MDF plate into position, clamp it. The exchange the drill bit to the wanted diameter and drill the hole to exact depth or trough as needed. I must admit that the depth display of my Bosch PBD 40 proved to be very handy. Next you see both plates with already some flanged bearings mounted. Then the gears come into play. First the centre gear that will also be connected to the height control later. Then the four smaller satellite gears are placed. They use no bearings but I inserted a nylon washer between the MDF and the plastic (POM) of the gear to protect the MDF from wear. Then the 4 large gears that will drive the spindles will follow. The spindles are made to a length of exactly 110 mm on the lathe and then the ends are reduced to 6 mm diameter for 4 mm so they will fit into the flanged bearings. You can also see an aluminum ring to adapt the spindle diameter to the 10 mm hole in the gear. I glued in 2 pins that will fit in a groove of the gear to drive the spindle. That’s the gearbox. It is covered by the second MDF plate. You can also see 4x a 3 mm pin with a plastic spacer that will keep the 2 plates parallel and at a distance to give the rotation parts a little play. As it is shown here it all looks simple. Believe me, it required a lot of tuning on all parts to get this whole mechanic move smoothly. Enough for today, next time the side plates and the height table will be added. Best regards, Kris

OK Bruce, you may take the front seat. For wooden model ship building you often need small pieces of wood in different thicknesses. That inspired me to develop a small drum thickness sander that would be easy to build and operate. My requirements list is however long: stiff drum to carry standard sandpaper material (no sleeves) easy mounting of the sandpaper on the drum (no gap in the drum) wide choice of grids easy drum exchange drum drive with variable speed support table that can be moved up and down while staying parallel (no tilting) precise height adjustment possible (resolution 0,05 mm) minimum sanding capacity: 100 mm wide and 20 mm thickness sanding down to 0 mm thickness should be possible efficient dust extraction When looking at this list I realize that I actually want to build my own Byrnes Thickness Sander but in a luxury edition. From the start I already had an idea of how the whole construction could be made. But before starting the build, I wanted to check if I can make a wooden drum that has a strip of sandpaper wound around it and fixed at both ends in an easy manner. So here we go. I started with looking for a suitable round piece of wood and ended up with a beech banister of 45 mm diameter and 1 m long. See next picture. I then cut this beech rod into pieces of 140 mm length. That is about the maximum size I can fix between centers in my Taig lathe. I turned it down to about 43 mm and then had to do some work at the end sides. The next image shows a 3D model of what I was trying to achieve. The narrow cut was made with a pull saw (at an angle of about 10° with the end side). It is 5 mm deep where it meets the drum surface. The rounding to the drum surface required a small sharp chisel. The centre hole of 6 mm diameter was made on the lathe and the hole touching the narrow cut is 5 mm in diameter and made in a drill stand. The groove in the middle was made on a Proxxon drill/mill stand. The result is shown next and is ready to be finished in a sanding drum. The sanding belt is 25 mm wide. I bought a box with 4 rolls of 6 m length in the grids 150, 240, 320 and 400. Wrapping the sanding belt requires a little bit of practice to get the start at the correct angle so that the turns will butt nicely without gap. Then a small piece of rubber tubing is placed in the 5mm hole and compressed with a screw so that the sanding belt is fixed. And finally the ends of the sanding belt sticking out need a cut. Done. I was pleased with the result and decided to go on with this project of building my thickness sander. best regards, Kris

In this topic I want to report on my effort in building a thickness sander. The last few months I spend some time finishing a second attempt that finally met with my requirements. But before I show the final result, I want to tell the story of the first attempt and comment on its construction and what I learned from it. In 2010 I decided that if I ever wanted to start a scratch build, I definitely needed a thickness sander. I got the chance to have a machine part available that seemed ideal to be converted into a sanding drum. It is an aluminium cast piece with bearings holding a spindle with rubber drum ( 35 mm). The drum was made thicker with some pipe insulation foam and a plastic tube over it. Then a sanding belt was glued on with double coated tape. The next picture shows that part with the sanding paper mounted. Next I needed an adjustable height table. I constructed a double scissor type jack from some copper pipe and aluminium strip (see next picture). An M6 thread, mounted in the middle of the copper pipes served as the height control. At the side of the table I added bronze bushings that glided over some vertical pillars mounted on a base plate. The next picture shows that whole construction. The sanding drum is driven by my drill held in a horizontal fixture. As soon as tried this setup it became clear that the whole table construction was a bad design because it got stuck at the pillars very often. A little tilting of the table was enough to block it. So I needed to rework it. I removed the 4 pillars and added an extra M6 thread. These 2 M6 threads are positioned at the sides close to the scissor construction and are synchronized with a timing belt. That setup is shown in the next picture. That setup did work quite well, but: - it is (too) large - needs mounting/unmounting of the drill - makes a lot of noise - lacks dust collection and removal - renewing the sanding paper is impossible without dismantling the drum construction - height control is intuitive (same turn of the knob will not result in the same change of the height) That is it for today. Next time I will show a different design that fits better to the needs of a model maker. best regards, Kris

When looking at the deck pictures, I almost forget it's a model. Fantastic detail and superb metal work.

Hi Tony, The micrometer shows no play nor backlash, so it should be precise up to 0.01 mm. I paid much attention to mounting the support very level both horizontal and vertical. In order to make the fit between the proxxon body and the support almost perfect, I filed the rounding by hand. But that was not perfect, a little tilting was still possible. So I decided to use some metal epoxy glue on the edges of the support and stretched some plastic kitchen foil over the proxxon top. After positioning the support on the plastic, I checked with a level tool and let the glue harden overnight. That resulted in an almost perfect fit without play. I still have to test its actual precision. As you might know 'the proof of the pudding is in the eating'. Kris

I have an MB200 drill stand from proxxon and I mostly use it for precision milling work. As a drill stand it only has a handle to do the setting of the depth that is indicated by a mm scale. For small depth settings below 1 mm it becomes difficult to adjust the depth to the wanted value. So I decided to improve the MB200 and fit an auxiliary depth feed screw on top. AS depth feed screw I use a micrometer head with 13 mm range (bought in China for 9 euro’s, but works very well). All the other parts to fix it on top of the MB200 are aluminium that I had available (piece of 40x20mm rectangular profile, 2 mm thick and some 5 mm thick flat extruded profile). Here is a model of what I tried to make. It is just a support (the rectangular alu profile) that needs an inside rounding at its bottom to fit the die-cast aluminium body (R=40 mm) of the MB200. On top of that there is a lid with 2 holes (20 mm apart) to mount the support with 2x M4x35 to the body. It also has 2 holes with M3 thread to fix the micrometer holder plate in 2 positions. Here are the machined parts. Next you see the MB200 with the 2 marks where a thread M4 is to be made and in a larger drill stand just before drilling with 3.3 mm. Then I only need to show the end result. The micrometer head can be mounted in 2 positions. Straight for milling and at 90° for drilling. For milling I remove the handle and after a depth adjustment you always need to lock the set screw of the dovetail again. I hope anyone in need of fine milling and owner of a proxxon MB200 can find some inspiration here. Best regards, Kris Avonts

Hi hyw, That's a nice piece of machinery. Based on the size of the square (250x160) I estimate the sanding disk to be 125 mm in diameter. The table is 200x100 mm (?) and sits on a linear guiding rail, but how do you tilt it? And a last question: this seems to be a 3-phase AC induction motor with frequency converter, but what is its power rating. It looks quite heavy for working with wood pieces of the size most used by modellers. Anyway... this is well done. regards, Kris

If you are looking for mica, take look here: I tried to cut mica and found that you can also split it into thinner pieces (kind of peeling off). Then it also gets easier to cut with a knife, chisel or scissors. To find where you can buy mica as it is used in electronic circuits, just google 'TO-3 mica insulator'. regards, Kris

Hi Dave, Indeed small parts are a real challenge. In your case I would do the following steps: Its just an idea, I have no experience with soldering such small parts. best regards, Kris

Mica is a good choice if you can find some clear samples. They are still used in electronic circuits to (electrically) isolate power transistors from aluminium (aluminum for the US folks) heat sinks. So you can find them in shops where they sell electronic components (or the internet of course). Most popular will be isolation sets for TO3 or TO220 style packages for power transistors. Here are some sample pictures. A typical TO220 mounting kit: These mica plates are 13 by 18 mm and about 0.15 mm thick. Also a remark on cutting the thin glass cover plates. If you want to cut these you need a fine point diamond scriber. Something like this: With some practise it should be possible to break the glass with a straight cut. During good scribing you can hear the glass cracking by the heat generated at the contact spot. It should not break however. Then turn the glass over (scribe down) and place on a flat surface of material that is slightly compressible. Place a small (ground) metal rod over the scribe and press it down gently.... crack, your plate is split. so far my 2 cents on this topic, best regards, Kris

Well Ab, you can pass my thanks to Rene also. And you deserve also credits for showing us these tricks so clearly. For me this is a real eye opener of what is possible with DELFTship. best regards, Kris

As I further explore FreeCAD, I want to share the next simplification to my proposed method in post #10. The polylines of 2 segments can be dropped completely, just constrain the three control points of the spline with symmetry. That will bring them all three in line and then you can make the middle one coincident with the target (offset) point. Done! The more I explore FreeCAD, the more I start liking it. Its GUI with the different workbenches is a bit awkword and not as coherent as a commercial product but it's free software and all files stay yours. I hope this helps some more FreeCAD users. best regards, Kris

You go really fast TonyM. But you should when I read about all your plans. Especially the idea of use 3D-printing to make jigs or plug is appealing to me. My intentions on the other hand are a little different. I want to reconstruct the hull in 3D based on an existing ship plan by using as much as possible the same construction techniques that the original artists uses. For instance if I know that the bottom of a frame consists of 3 sweeps (arcs), I will draw 3 sweeps and no spline. I'm sure it will my 3D work harder but I will give it a try. best regards, Kris

In addition to my sketcher B-spline workaround I have to warn that the curvature of the resulting spline is much less fluent then the one that is drawn with the multiple-point B-spline tool from the draft workbench. See the next screenshot (magenta is draft spline curvature, blue is sketcher spline curvature). The explanation is simple. The points from the sketcher spline that I made coincident with the offset points all have zero curvature in that point. In a fluent curve zero curvature should only be present in inflection points where curvature switches its sign. The general curvature trend along the spline is however almost identical. So if you don't seek the utmost curvature smoothness, the sketcher spline will do fine because it maps very close to the station line. all the best, Kris

Hi TonyM, I think I can show you a way to get the splines for the stations to pass through your offset points. I also do it as an exercise for myself to get more confident with the sketcher and/or draft workbenches and their capabilities. First I extracted station 5 from one of your screenshots, removed most of the background and inverted your resulting white B-spline to black. That image was then imported in FreeCAD with the image workbench, scaled and moved. I scaled to some arbitrary size so I could use your numbers for the position of the offset points in mm units. Then I started sketch000 to define your offset points. The vertical line is a polyline with its lower point at the origin (coincident constraint) and then vertical distance constraints for every other point are added. Next are the horizontal lines added to reach your offset points. To make the desired B-spline, I started a new sketch, sketch001, and imported the horizontal lines from sketch000 as external geometry. Now the actual work can begin. First I tried the work around form the FreeCAD forum I mentioned in the topic ‘Need CAD type program’ (https://forum.freecadweb.org/viewtopic.php?t=30180#p249022).That was a disappointment because it resulted in lots of errors being reported and even complete crashes (stop reacting) of the FreeCAD program. Then I invented my own work around that I will describe next. Draw a B-spline along the profile of the station. Start with a point at the top about the same height as your highest offset point, then 2 intermediate points are placed on the way to the next lower offset point. Then 1 point next to the offset point. Again 2 intermediate points on the way to the next offset point where again 1 point is placed and so on until you reach your lowest offset point. This results in 22 control points in this example. Then I switch to construction mode and draw polylines of 2 tangent (press 2x M key between 1st and 2nd line) segments along the spline at each offset point except the highest and lowest. Now I constrain each polyline with symmetry. Next I constrain all polyline points to be coincident with the corresponding spline control points. Now we can put the spline over the station line by a coincident constraint for the endpoints and the points that correspond to offsets. That looks awful but we can touch up the spline by moving the intermediate points into position until our spline pleases the eye. The result looks like this. Now you have a sketched station line that passes through your offset points. Just to compare, I also used the draft workbench to draw a B-spline through points with the end-line snap active. You see the draft B-spline in magenta colour and the sketcher B-spline in light blue. They are almost identical. For me this was a pleasant exercise and I hope you can use some hints from this example to refine your model. Best regards, Kris

I want to share the current state of my FreeCAD work. It is for an English third rate ship (74-gun) from the second half of the 18th century. I must admit that it is a far too complex ship to start with, but my desire to bring such ship to live won from logical reasoning. Here we go: It is just a bunch of points. I used both draft points and part vertices. The exact difference between the two kinds is unclear to me. They are arranged horizontally along the waterlines, half-breadth lines, top-timber line and topside. Vertically they follow the location of the stations. The next picture shows this more clearly. I made curves through these points both with draft splines and the tools from the curves workbench. I wanted to use the Gordon-surface tool from the curves workbench to skin the network of curves. That was a disappointment and only resulted in errors. My network of curves, that looks quite OK visually, is far from a real network because intersection points of horizontal and vertical curves are actually not coincident. I think you can only get that by using sketches that import these intersection points from external geometry (sorry if this sounds very FreeCAD slang). My tree-view of this model also lacks structure and that makes it difficult to keep track of more then 300 points already. Conclusion: I will try to start over the effort and use sketches from the start. best regards, Kris