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Finding sheaves for small functional blocks?


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Does anyone know where I could find or how I could make a sheave for a functional block?

 

I'm trying to rig an RC model to use working blocks for use with the running sheets, but I'm using the blocks that came with the kit, which are little more than a piece of wood with a hole drilled into it. I've tried to sand it down and enlarge the hole to make it look more realistic and have less friction on the line, but it's still not adequate and routinely kinks up. I'd like to make a true functioning block with a turning sheave inside it, but I'm not sure how to make one on my model's 1:25 scale. I know how to fashion the wooden part and the axle, but the sheave would be about 1mm thick with a diameter of about 2mm, and I don't know how I could make anything that small with enough precision to be useful.

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41 minutes ago, FoxtrotHotel said:

I don't have a lathe, and really don't want to buy one to make my own.

Yeah a few pieces is not a good reason to spend hundreds of dollars. Do you have a rotary tool or cordless drill? Lots of people make very nice turned parts by chucking them either in a Dremel tool or a cordless drill depending on size. All you need is a round needle file to shape the sheave correctly and then you can saw them off one at a time. 

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I am wondering about the dimensions of your sheave, i.e. 2 mm diameter and 1 mm thick. This is rather thick for the diameter or rather small for the thickness. Proportions change over time, but a relation of somewhere between 1:5 or even 1:10 seems to be more normal. In a sheave 1 mm thick the groove would be 0.5 mm deep, which doesn't let much much material for the axle.

 

Kit blocks are not likely to be a good starting point, as the shell proportions are usually wrong, namely they are too thick. I would check against sources for the period of your model.

 

Otherwise, yes the lathe would be the best option, a rotary tool the second best. For a working model you may want to look into some suitably coloured plastic, as this is easier to work free-hand than metal.

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8 hours ago, vossiewulf said:

 

Yeah a few pieces is not a good reason to spend hundreds of dollars. Do you have a rotary tool or cordless drill? Lots of people make very nice turned parts by chucking them either in a Dremel tool or a cordless drill depending on size. All you need is a round needle file to shape the sheave correctly and then you can saw them off one at a time. 

Interesting. I have both a Dremel and a cordless drill. I even have a Dremel attachment for using it as a drill press that can be mounted horizontally for use as a grinding station. However, I'm still not sure I could pull off that size of sheave. It would need to be not much more than 1mm-1.5mm in thickness but the smallest needle file I have is 2mm.

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4 hours ago, wefalck said:

I am wondering about the dimensions of your sheave, i.e. 2 mm diameter and 1 mm thick. This is rather thick for the diameter or rather small for the thickness. Proportions change over time, but a relation of somewhere between 1:5 or even 1:10 seems to be more normal. In a sheave 1 mm thick the groove would be 0.5 mm deep, which doesn't let much much material for the axle.

 

Kit blocks are not likely to be a good starting point, as the shell proportions are usually wrong, namely they are too thick. I would check against sources for the period of your model.

 

Otherwise, yes the lathe would be the best option, a rotary tool the second best. For a working model you may want to look into some suitably coloured plastic, as this is easier to work free-hand than metal.

I'm estimating the sheave size, as the kit plans don't show them. My kit is Corel's 1:25 Chesapeake Flattie. From the schematic, the block's overall dimensions I estimate are 3mm x 3mm x 4mm, which is pretty close to the small single-hole block provided in the kit.

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Well, then a rough estimate of the real block dimensions would be 4 mm long, 3 mm wide, and only about 2 mm thick. This means that the sheave should have a diameter of 2.5 to 3 mm and be only about 0.8 mm thick.

 

There are very fine round files in jewellers' supply shops, but they are pricey and difficult to get.

 

I think, if you are plan to stay in that business, the best thing would be to convert the electric into a simple lathe with hand-rest, using the horizontal stand as a starting point. There should be some examples for this on the Internet, or even here on the forum. For turning the grooves you then can use the back of a drill, ground to an angle, like a chisel and held in a pin-vice.

 

I know you Americans have a somewhat strained relationship with China these days, but the Chinese are selling on ebay very primitive miniature wood-turning lathes:

s-l1600.jpg

(Example from ebay offer https://www.ebay.com/itm/Basic-Edition-Micro-Lathe-Beading-Machine-Woodworking-Tool-Set-DC12-24V/153089968149?epid=9021229608&hash=item23a4df8815:g:5HkAAOSw~SNbQIdu)

 

You can buy one for around 40 USD or use its design ideas for setting up your electric drill.

 

I think, over here in Europe one can actually buy such sheaves from model supply houses. Not sure, though, as I would turn them out on my own lathe.

 

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5 hours ago, Gregory said:

Cornwall Model Boats has a nice selection of brass sheaves.

 

I saw some 2mm ones, as well as these brass blocks, that may not be the look you want..

 

I have ordered stuff from Cornwall, and surprisingly, the shipping cost is not bad for small items..

 

 

How about buying a few of these brass blocks in a size you can use (they list 2, 3, 4, 5 & 6mm) "liberating" the sheaves and building your own blocks around them?  That would obviate turning them.

Just a thought,

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This is not such a difficult thing to do.

 

First, buy some 2mm diameter brass rod. One good source is Scale Hardware https://model-motorcars.myshopify.com/collections/the-metal-shop/products/9863-2mm-diameter-round-brass-rod

 

Cut off a short piece and chuck it in your Dremel. Mount the Dremel in a vise or some sort of holder so you can use both hands to hold a small file.

 

Use a triangular file to score the groove. (The groove really doesn't have to be semi-circular.)

 

Slice off a 1mm wide piece with a jeweler's saw. You will probably need to run the cut side over a file or some sandpaper to make it flat.

 

Center-punch the slice, clamp it in a vise (use some scrap wood to protect the edges of the groove) and drill the required size hole using your drill press.

 

Sheave number one, done. Well, your attempt at sheave number one will be done. It may take making several to get two that are good enough. But seriously, this just isn't that hard to do.

 

My two cents, anyway.

John

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1 hour ago, jhearl said:

This is not such a difficult thing to do.

 

First, buy some 2mm diameter brass rod. One good source is Scale Hardware https://model-motorcars.myshopify.com/collections/the-metal-shop/products/9863-2mm-diameter-round-brass-rod

 

Cut off a short piece and chuck it in your Dremel. Mount the Dremel in a vise or some sort of holder so you can use both hands to hold a small file.

 

Use a triangular file to score the groove. (The groove really doesn't have to be semi-circular.)

 

Slice off a 1mm wide piece with a jeweler's saw. You will probably need to run the cut side over a file or some sandpaper to make it flat.

 

Center-punch the slice, clamp it in a vise (use some scrap wood to protect the edges of the groove) and drill the required size hole using your drill press.

 

Sheave number one, done. Well, your attempt at sheave number one will be done. It may take making several to get two that are good enough. But seriously, this just isn't that hard to do.

 

My two cents, anyway.

John

I just did this yesterday, based on wefalck's similar advice. It came out ok and functional. The biggest problem I had was both clamping and centering the sheave for drilling the hole. I have no clamp that can hold it well nor get proper purchase, as well as keep the drill bit perfectly centered. I have one of those small desk vices, that I just tilted at 90 degrees and carefully positioned under my Dremel drill press. The result was my hole came out slightly off centered and at a tiny angle. It's barely enough to be noticeable, but it's enough to stop the sheave from freely turning. However, even stationary, it's still far less friction than a plain wooden kit block.

 

Does anyone know how I could reliably drill better centered holes on such a small scale?

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Clamp a piece of sheet stock on your drill press table (the Dremel press should work for this) and drill a hole part way through it with a diameter equal to the outside diameter of your sheave. Without unclamping the sheet, change bits to one the diameter of the shaft through the sheave.  Put the sheave in the hole in the sheet and drill the hole for the shaft. It should be exactly centered in the sheave. Then pop the sheave out of the jig ( you might want to use a shaft through the center hole to wiggle it out) and move on to the next sheave.

 

Vince

Edited by VinceMcCullough
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27 minutes ago, VinceMcCullough said:

Clamp a piece of sheet stock on your drill press table (the Dremel press should work for this) and drill a hole part way through it with a diameter equal to the outside diameter of your sheave. Without unclamping the sheet, change bits to one the diameter of the shaft through the sheave.  Put the sheave in the hole in the sheet and drill the hole for the shaft. It should be exactly centered in the sheave. Then pop the sheave out of the jig ( you might want to use a shaft through the center hole to wiggle it out) and move on to the next sheave.

 

Vince

I tried something very similar to this, but the problem is the sheave just spins when I try to drill the hole. The cutout in the stock keeps it centered, but the sheave isn't actually clamped, and it's too small to get a clamp securely on it.

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How about if you chuck up a piece of the 2mm rod with the end centerpunched, in the Dremel, in the drill press, and then firmly chuck, clamp or whatever you have to work with, the bit for the center hole, taking care to get it vertical and lined up with the dimple in the end of the rod. 

 

Lower the spinning rod down onto the stationary bit, and drill a hole deep enough for a few sheaves.

 

File a groove, part off a sheave, and continue, deepening the hole as required, until you have enough to mess some up and still have enough to finish the job.

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3 hours ago, Altduck said:

How about if you chuck up a piece of the 2mm rod with the end centerpunched, in the Dremel, in the drill press, and then firmly chuck, clamp or whatever you have to work with, the bit for the center hole, taking care to get it vertical and lined up with the dimple in the end of the rod. 

 

Lower the spinning rod down onto the stationary bit, and drill a hole deep enough for a few sheaves.

 

File a groove, part off a sheave, and continue, deepening the hole as required, until you have enough to mess some up and still have enough to finish the job.

That's an interesting idea. You're right, clamping the pre-cut rod would be a lot easier than clamping a tiny sliver.

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To follow up on post #20 - something an old mechanic showed me, whoe run the students' workshop at my university: take a piece of thick stock, somewhat wider than the diameter of the sheave, clamp it into the vise and drill a hole a few millimeters deep (preferably with a wood drill to give a flat bottom) with the diameter of the sheave, change the drill to the diamter needed for the axle, drill right through, take the piece out and with a piercing saw cut a slot all across the the seat for the sheave and beyond. Now when you clamp the piece in the vixe again, it will be slightly compressed and hold the sheave tight for drilling.

 

(I love my watchmakers lathe and milling machine, for which I have collets and arbors, that can hold such small parts for machining without the need to make jigs ... 😏)

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... that's why I put the comment in brackets ;)

 

My brass spur gear (for an anchor whinch) was actually about 8 mm diameter and he used an 8 mm end-mill to make a recess in a piece of scrap aluminium. I think with a piece of hard wood, a 3 mm (which is what he needs), and a jewellers piercing saw and a very fine blade it should work.

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Let me give you one more possibility.  Clockmakers supply houses used to carry "bushing wire" which is basically thick walled brass tubing in small sizes.  I don't see it anymore in US vendors' catalogs, but Meadows and Passmore in the UK has this:

 

http://www.m-p.co.uk/muk/parts/chap10/bushing-wire-x-2pcs-1.75mm-od-0.50mm-id-0558017515.htm

 

and this:

 

http://www.m-p.co.uk/muk/parts/chap10/bushing-wire-x-2pcs-2.50mm-od-0.65mm-id-0558025015.htm

 

They offer a range of sizes from 0.80 mm to 5.0 mm but unfortunately, no 2.00 mm OD but if you can fudge on your scale size a little, you get the rod pre-centerdrilled and just have to groove and part it off.

 

Good Luck,

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