Author Topic: Flycutter design  (Read 9880 times)

Offline andyf

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Flycutter design
« on: January 28, 2011, 10:07:29 AM »
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
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline J Harp

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Re: Flycutter design
« Reply #1 on: February 02, 2011, 02:49:43 PM »
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.
Jim

Offline maybecnc

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Re: Flycutter design
« Reply #2 on: February 02, 2011, 04:20:04 PM »
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
Latest project: Modifying chucks for front monting  http://www.toolsandmods.com/mini-lathe-chuck-backplate.html

Offline andyf

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Re: Flycutter design
« Reply #3 on: February 02, 2011, 07:41:09 PM »
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
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline maybecnc

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Re: Flycutter design
« Reply #4 on: February 03, 2011, 05:22:58 AM »
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
Latest project: Modifying chucks for front monting  http://www.toolsandmods.com/mini-lathe-chuck-backplate.html

Offline andyf

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Re: Flycutter design
« Reply #5 on: February 03, 2011, 08:29:17 AM »

..... 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.

Jose

Hi Jose,

That's very like what I have done, except that I bolted the piece back on the bottom, leaving a square tunnel for the tool. At speeds up to 800 rpm, it seemed fairly close to balance, and worked well, and that is about the highest speed at which the tool will be used. I was truing up the slightly convex sides of some square aluminum tube, and I thought somewhere around 400 surface feet per min. would be right for aluminium. 800 rpm with the tool sweeping a 2" circle gave me around 400sfm for the final 0.002" deep pass. The first roughing cuts, about 0.01" deep, were done at about half that speed.

The tube is to form part of the casing for a power feed on the mill. After several sessions of 20 minutes each, very slowly traversing the table by hand over a distance of 11" with my feet getting colder and colder on the concrete floor, I have decided that a power feed is definitely a good idea!

Andy
« Last Edit: February 03, 2011, 04:31:30 PM by andyf »
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline bp

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Re: Flycutter design
« Reply #6 on: February 03, 2011, 03:39:52 PM »
To avoid vibration the flycutter that I saw at work was about 125mm (say 5") in diameter about 20mm (3/4") thick steel, a big flywheel.  The cutter was a piece of 3/16" HSS inserted at the periphery at about 45 degrees, with only about 3mm exposed to do the cutting, secured in the steel disc with one or two set screws.  This was run at high speed with a fairly shallow cut.  It was used on a B'port, and on anything that required flycutting, steel, aluminium etc.  The finish that I saw on a piece of 6061 T6 was almost optical.
Whilst I must admit I've planned to do something like Andy, only with an MT3 blank arbor to better fit my X2, I've often wondering about making a bigger diameter one, maybe 50mm diameter.
cheers
Bill Pudney

Offline andyf

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Re: Flycutter design
« Reply #7 on: February 03, 2011, 04:54:10 PM »
Bill, I must admit that the range of mine is a bit limited. With the 38mm blank ended arbor I used, the minimum swept diameter is (with a bit of cheating, like shims above the tool) about 40mm. The max is about 80mm, though that would involve the tool protruding 16mm - perhaps a bit too far for comfort, especially on hard materials. Perhaps that's why commercial ones often come in sets of three different sizes.

Mine was made from a 38mm arbor because I already had one, and it was just the right size for the job I wanted to do. For me, it's only rarely that things turn out so serendipitously (that's my word of the week).

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline maybecnc

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Re: Flycutter design
« Reply #8 on: February 03, 2011, 06:34:54 PM »
That's very like what I have done, except that I bolted the piece back on the bottom, leaving a square tunnel for the tool.

Andy,

Oh, you did it. I was thinking you have bolted 2 small parts with the slot. But of course it wouldn't make sense to mill first.
So it works ok. That's good to know.

Jose
Latest project: Modifying chucks for front monting  http://www.toolsandmods.com/mini-lathe-chuck-backplate.html