Hobbies Cam Fretsaw (Reverse Engineering)

This is a hobbies fret saw, in fact these are two fret saws. The thing that makes these quite unique is the cam on the top of the saw that you can use to tension the blade.

I bought one from a market in Vauxhall and the other from ebay. And they sell for roughly around 5 to 10£ maybe £15 depending on condition.

One is an original hobbies saw with a maker’s mark on the metal, while the other seems to be a clone. The clone is missing a few parts but the design still works.

This one was missing the tightening screw. It also happens to be a bit shorter.

If you were to buy the modern equivalent of these saws – sold to jewellery makers and dovetail enthusiasts, you would be spending quite a lot of money. Up to £100 depending on the size.

I think I’m going to take one of these apart, and identify the shapes used to actually assemble this. And see if I can make one myself.

I’m going to make a clone, of the clone.

So I am going to dismantle this saw, and I’m going to start by tapping and drilling out the rivets.

I have to hammer that out.

I had to file some of the rivets as the drill bit began to slip off.

So this is all the parts for the Hobbies saw minus one of these which didn’t come with the one I found in the market. And there should be another one of these, which is in there. I think that’s all the parts but I might have misplaced something already. I’m going to flatten all the sections out now so I can trace them and create some cut lines to follow.

So these two should be the same so there’s no point in me drawings both of them out. I might as well take one and mirror it when I go to scan it in.

I took measurements of the thicknesses of various parts and later scanned the image into a computer.

This is going to be the hardest bit to make. I may end up having to redesign these. So those are the parts for the Hobbies coping (fret) saw. What I’m going to do now is scan this image in and import it into fusion 360, and actually trace over the lines to produce a 3d model of the different parts.

I had to calibrate the image by selecting two points and comparing the measurements with that on the paper. I could then begin sketching over the lines and extruding the new plate parts. Here you can see the plates superimposed on the drawings that I imported as a canvas. I’m actually going to export the individual sketches as DXF files and then import them into artcam where I create my tool paths. You can use fusion360 to create tool paths but since I know one software already I’m not going to go down the route of learning another one (just yet).

I’ve got piece of aluminium from an apple computer. There comes a point where the material becomes more valuable than the machine so I might as well use it to make a fret saw. I’m just going to cut this out so I’ve got a nice rectangle with not too many raised bits.

Ok so this is about 1.5mm so I think I’m going to have to double up some parts especially the actual “C” kind of… The frame. It’s called a frame. I don’t have enough material to double up the frame, so I’m just going to cut it out and see what happens.

I didn’t set a pecking toolpath for the initial holes. It was just trying to go straight through so I stopped it and edited that toolpath and I’ll have another go.

I used a drill toolpath with pecking – and retraction at 0.2mm to help make the through holes. It’s something to do with the geometry of the bit or maybe the plunge rate is still set too high, but it doesn’t like to plunge straight through the material.

In case anyone is interested I’m cutting at a step down of 0.2mm with a 1/8 of an inch bit, at a feed-rate of 200mm/min, a plunge rate of 80mm/min and a spindle speed of 15000 RPM.

Of course if you don’t have a CNC machines you could use that other type of CNC machine called a printer to produce templates which you could stick onto the material you want to cut.

Ok it all looks like it has cut out pretty well. I had to redo some of the toolpaths, just so I could get a bit further through. You can see a little wafer of aluminium left behind in a few plates. Obviously it’s not entirely flat but everything looks pretty good. It’s quite late now so… what I’m going to do is basically move the bit back to the origin position. I wont be in for a few days – until Saturday, and then I can have a look at this with a fresh pair of eyes and check in case I’ve accidentally missed something out. I haven’t gone all the way though with these holes just coz difficult to actually get the material out with the type of bit I’m using. That said I’m really impressed with this so far.

Ok it’s Saturday, I’m going to try and finish drilling through the holes, for the different pieces. I’ve left it several days and before I felt on the Tuesday I made sure the bit was back from the origin position under there. And this will be a good test to see if anything the machine has shifted over the several days. Bit of a gamble as well coz if it starts to drill anything out in the wrong position, I’m going to have to stop it very quickly.

Nathan: You can possibly get the compute a bit closer.

That’s quite a satisfying noise.

This does feel a little bit flexible but I could always reinforce it later.

Ok these are all the components. I’ve just filed them to get rid of any sharp edges. And I’m going to attach them now with small machine screws.

Everything came together quite nicely and the object being made in aluminium looked very sleek.

Now I need to bend this piece of metal into this shape.

Ok I think I’ve just saved it, the tab is in place there. Bit tight. I’m going to file these corners here. So they are a bit flatter and wider.

Ok I manged to get one on, but it doesn’t look particularly great. I just have no idea how they would have made that shape without I guess making some kind of former and having a big press.

It still doesn’t feel right. It’s not the right shape. And I can’t even open the tab here. There should be a gap there where I place the fret saw blade. I think I’m going to have to take this off, as I said earlier cut some more of these or think of another solution.

I really struggled with bending the metal into the desired shapes. Every time I attempted it, I seemed to get worse. I guess I could have approximated the negative space of one example and CNC’d that out to use as a former but I was getting little impatient.

What I’ve decided to do is just 3D print this instead so I’ve modelled it fusion 360. Exported it, put it into repetier host and I’m just going to print it out and see if it works. .

Ok the 3d printed section of this fretsaw is done. This is the second version. I’ve had to file out the notches along here so they were a little bit bigger. And the tab, which is this thing here. Is a little bit tight still, but it seems to come together ok. So I’m just going to assemble this.

Well the design definitely works. It’s just the material’s a bit flimsy. I suspected something would go wrong, but this almost looks like a novelty fretsaw now. When you tension that up the actual bar flexes. You can see the shape that it turns into. I think what I should have done, or what I should do if I were to carry on with this project. Is to take this section up here, and that section down there and extend them to follow along the frame. Which I can fix onto onto the side and the added material should help that become more rigid. Interestingly the 3D printed parts seems to be holding well. This is only PLA. I’m sure if I did with with ABS, it would be a little more tougher. I’m going to try cut something as well.

Ok I though I’d just try the old back on the saw and it’s actually made a difference. I can actually tension this a little bit. Ah it’s slipped out there. Argh the 3D printed part broke. Dam it. It’s lasted half an hour. A good proportion of the time you spent making it. If I can work out how to make these sections out of aluminium obviously it will be a lot more durable.

Anyway, this video has come to a natural end. I might come back to it in the future, or not. But what I’d like to do is make the files available – so that someone else, with a little more time and skill at bending mental, can have a go at making a clone of the clone. So the link to those will be in the description. As usual thanks again for watching and don’t forget to sacrifice a thururururur.

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