How best to cut out bulkheads?

[twintrow]

As I mentioned in another post I picked up an Amati HMS Price  circa 1975. The kit comes in a wooden box nor cardboard.

And it was made before Laser cutting, even before die cutting.  One must cut out the bulkheads from 1/4" Plywood.

The basic bulkheads are not a problem and I have a Band saw with a 1/8" blade and a scroll saw as well.

Problem comes in to play cutting out the many "window like" openings (see photos).  I drilled a hole at each corner then using the scroll saw cutout the window by disconnecting the blade inserting it through the hole then reconnecting the blade.  Needless to say this is very time consuming, AND I'm getting some shredding on the far side of the hole even using the blade with the highest TPI and at moderate speed.   Again see photos.

There may not be any easier way to do this, but I'd appreciate any suggestions.  I've already talked with three laser cutters in Phoenix and all say the photo setup plus cutting will run near $500.00 so that is not an option.

Thanks for the help.

Tom

[mtaylor]

Tom,

What's the TPI on the blades?  Are you using a zero clearance insert on the scroll saw?  

 

I have 2 different blades I use for the thin stuff..

 

One is from Sawbird..  #3 Double Tooth Reverse  (the teeth at the bottom dont' cut on the down stroke but on the up stroke.  These are 20 TPI but I think they may have some with a higher tooth count.

 

The other type is from Olson.. Skip Tooth #400 with 33 TPI

 

Hope this helps.

[twintrow]

Thanks for the response Mark, the blade I used was 20 TPI.  I have a spiral blade I haven't tried yet.  Someone suggested it especially for cutting out the window like features.

Tom

[thibaultron]

You could also place a sacrificial board behind the plywood.

[Jaager]

1.  As I have written here several times - check the keel length on this kit.  It may well be the one where the draftsman for the kit plans  confused touch with LBP.   Most data for the ship taken from 17th Century sources will give the length as touch.   For the 18th Century on it is LBP.  If the hull is too short,  the additional length can be patched in at the deadflat and the middle bulkhead replicated - one fore and one aft.

 

2.  The thin ply will not offer much support, plank attachment surface, or resistance to warping.  Why not wood glue the existing bulkheads to a thicker piece of plywood - or a Basswood sheet.      The extreme would be 3/4" Birch ply  - which would be a bear to scroll cut, but make a strong base.  Getting the bevel right, will take more work and planning if you want the whole edge surface to support the planking - rather than the knife edge that is designed with the kit.

[justsayrow]

Masking tape on the backside of the part helps too.

 

I usually drill closer the the center of the window, then cut diagonally into each corner. That seems the help give it relief when I cut along the lines.

[mtdoramike]

I have always used a coping saw, which is a lot of hand work, but I have found that I can speed up or slow down as I need and I have a lot better control over the cut than with a scroll saw. I have owned two scroll saws, a Harbor Freight and a Craftsman and neither one was worth a plug nickel.

 

Try a coping saw, I think you will have better success and their about $5.00. But I believe the problem is coming in with the age of the kit and the plywood, which appears to be possibly separating due to failing glue. If this is the case, you may have to make new bulkhead patterns on new wood if the kit came with the patterns drawn on the plans at full scale. I know you probably don't feel this way now, but you are one lucky individual being given the opportunity to build this older beauty. Good luck with the build and look forward to plenty of updates.

 

mike 

Edited February 11, 2016 by mtdoramike

[Jaager]

If you copy the bulkhead patterns using a scanner and your computer printer, you should make sure that these devices do not alter the scale with their copies.

 

I scanned a transparent 6 inch / 15 cm ruler and printed it out.  To get the printout to match the original ruler required an increase in scale of the scanned JPEG =  x 102.5%.  This has proved to be consistent for all scanned images.

[Moxis]

As Mike suggests, use coping saw. And thin saw blades, the ones which are intended for jewelers. For example these

 

I have also tried to use the scroll saw for this work, but it doesn`t work. Then I changed for coping saw and have used Vallorbe Glardon blades for years without any problems. The thinnest and smallest items can be sawn without any problem anytime. Although I use their thinner grade 6/0 blades, the 4/0 grade are quite usable too and do not break so easily. And be sure that the blade tension is tight enough, if loose the blade will break easily.

[twintrow]

Thank you all for your suggestions.  I think the coping saw may be the way to go.  At the time the kit was made that was probably the intent.

 

 

Has anyone used spiral blades??  How well do they work.  The concept seems firm but only applying it will tell.

 

Tom

[Moxis]

Has anyone used spiral blades??  How well do they work.  The concept seems firm but only applying it will tell.

 

 

I have. They do not work, are too coarse. TPI for those jeweller`s blades I use is 67 or more, spiral blades are something like 20. They will rip the underside of plywood no matter how careful you are.

[twintrow]

Great Moxis thanks for the heads up.   Saved me the experience AND the cost.

Tom

[texxn5]

Have you tried using a Mill Bit say from 3-5mm with side cutting abilities in a drill press with good tolerence control? Might be worth a try.

[jre8655]

Tom,

 

I'm not sure if a Coping Saw is route to go.  The spiral blades are hard to control and as mentioned are very course.  The Jewelers Saw Blades are somewhat expensive and I have found Scroll Saw Blades that are finer.

 

Several suggestions:

 

Try using automotive masking tape on the back side of the plywood.  It has a very fine grained adhesive and should not harm the wood.

 

I've used scroll saw blades from Woodcraft that are up to 46 tpi and found they cut very cleanly with a minimal splintering on the back.

Here is the URL:  http://www.woodcraft.com/category/PA115-08-01/scroll-saw-blades.aspx?gclid=CKqOz5GY9coCFQoNaQodwj4PiA

 

And one question.  What kind (brand) of a Scroll Saw are you using?

Edited February 13, 2016 by Jack Tar

[twintrow]

Jack....Ryobi 16" variable speed scroll saw.  The 46 tpi blade is what I referred to as a spiral blade.   I'm thinking I recently bought a micromark small x-y table ($110) for my small drill press, maybe try that like Texxan5 mentioned.

 

Tom

[jre8655]

Tom,

 

I'm not so sure I would try using the drill press/x-y table to cut out the bulkheads.  Here's why:  it's very easy to turn the adjustment knob the wrong way, thereby risking cutting in a direction you don't want to go.

 

Now there is another way to do this...use the x-y table to move the cutting tool to a precise location then drill a hole.  Repeat this all the way around the section you want to cut out, drilling a series of holes then just cut between the holes to remove the section.  It wouldn't be much of a chore to file and sand the bulkhead after that.  I've done this with some difficult pieces in the past and had very nice results.

Edited February 14, 2016 by Jack Tar

[reklein]

The double cut blade is to me the best suggestion here. The teeth on the blade will cut upwards on the bottom and downwards from the top. Rule of thumb is to have at least 3 teeth on the thickness of material. If cutting 1/4 inch stock then at least 12 tpi would be sufficient. too fine and your blade won't clear out the sawdust and cut slowly and heat up. As for repeatedly detaching the blade and reattaching it for all the holes. Well, that's just a necessary part of the challenge.I would also suggest going to your local book or grocery store and find the magazine Scrollsawing and look up blade suppliers,and read the hints and tips sections. You may even find a book on scrollsawing that will specialize in projects, tuning your saw and hints and tips on accurate cutting. Just scrollsawing alone is a fairly popular hobby.   Bill in Idaho