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Flycutter design

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andyf:
I've had an MT2 blank arbor with a 1.5" diameter soft end loafing around for some time, so decided it ought to stop being lazy and do something useful, hence this:



The tool shown is only in there for the photograph. The tool-slot is off-set slightly so that one side of a tool blank (the top, in lathe terms) will automatically have a 7o rake, though (again in lathe terms) side rake will still be needed.

I know balance isn't too much of an issue at the relatively low speeds used with these tools, but to my mind it would have been better to have left the end flat, rather than cutting it off at a 20o angle, and simply milled the toolslot so it was deeper at one end than the other.

I understand that some commercial flycutters have their shanks offset to compensate for the imbalance caused by the sloping underside, but can anyone tell me if there is a good reason for having a slope there in the first place? The only one I can think of is that it allows one to see the workpiece beneath as the flycutter rotates.

Andy

J Harp:
Andy; thats a fine looking flycutter. Sorry I can't help with the balance question as I'm no good at math. Surely someone good at math could figure out how much the shank would need to be offset to bring the head into balance.

maybecnc:
Good looking Flycutter!

Yes Andy. I have made a couple and leaving the end straight is the way to go to keep it balanced. Also the bigger the angle for the tool, the more unbalanced it will be. 10 to 15 degrees works fine for me. The bigger one (35mm dia) with 10 degrees works really good. I haven't yet made another couple of flycutters  with straight end, but that's on my list.

http://www.toolsandmods.com/flycutter.html

andyf:
Hi JH and Jose,

It was very easy to make, starting with an MT2 arbor as shown at the top of this page http://www.arceurotrade.co.uk/Catalogue/Blank-End-Arbors (mine was 1.5”, or 38mm).
1. On the lathe, with the arbor in an MT3/MT2 adaptor, drill the centre hole already present in the end of the arbor to a greater depth, to give a rough idea of where the centre was after step 2.
2. Saw off the bottom at a 20º angle (with hindsight, I should not have done that)
3. Grip the flats in the milling vice, with the sawn edge approximately horizontal, and clean up the sawcut.
4. With the job still in the vice, mill out the offset tool slot, 6.5mm wide and 6.5mm deep (to allow for both 6mm and ¼” square tools). I drilled a line of holes first, so the slot-cutter would have less work to do.
5. Replace the job in the vice with one of the flats on parallels (actually, I don’t have any parallels, but for this job anything which is fairly parallel will serve), mill out two slots for the heads of the Allen screws to clamp the tool, then drill and tap M5.
6. Clean the whole thing up.

When I ran the flycutter over about 300rpm, vibration began to set in – hence my first post. Subsequently, I searched the floor for 20 minutes, and finally found the piece sawn from the bottom in step 2, cleaned up the sawn side and bolted it back on with M3 Allen screws, to produce this:   



Yesterday, I cleaned up a length of 2” square aluminium tube at about 800rpm for the finishing pass. Very little vibration, and the finish was acceptable. 

What I should have done after Step 1 was not to have sawn off the end at an angle, but just mounted the job in the vice at a 20º angle for cutting the slot in Step 3. This would have reduced the imbalance to that caused (a) by the tool itself, and (b) by the wedge of missing metal below the tool at the end where the slot was deeper. Mike of http://mikesworkshop.weebly.com/ suggested a simple cure for (b) : a wedge of steel pinned in place to fill up the gap under the tool.

Andy

maybecnc:
Andy,

If you want to try what I would like but I can't...

I don't do silver soldering, but you do. You can make a new flat end for it and silver soldering it to the flycutter. Finishing it after that on the lathe/mill.
This way you can put metal back covering the milled slot. You will get a nice flycutter with a square hole for the toolbit and a minimum amount of removed metal from it.

That should make the flycutter quite close to balanced.

Jose

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