Help holding thin material for fly cutting

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seal killer
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Help holding thin material for fly cutting

Post by seal killer »

All--

I've got a little piece of 3/8" x 4" x 5" aluminum that I need to hold for fly cutting. It has been chamfered, top and bottom on all four sides, so I only have 1/4" thickness to hold. My attempts to hold it in the Kurt so far have been less than optimal as when I tighten the vise I lose the level.

How can I hold this piece either in the vise or otherwise?

Thanks!

--Bill
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Bill Shields
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Re: Help holding thin material for fly cutting

Post by Bill Shields »

SUPER GLUE it to a piece of larger metal.

put a weight on it to SQUEEZE all the glue out and get as close to surface to surface as possible.

sometimes, I rough up the clamping block with sandpaper to provide a 'rough surface'...seems to help.

when finished, toss in the oven a 400 F and it will fall apart.

naturally - go at the cutting slow and DON'T OVERHEAT the part. this is one occasion where a mild air blast will really help.
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warmstrong1955
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Re: Help holding thin material for fly cutting

Post by warmstrong1955 »

Today's solutions are tomorrow's problems.
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Harold_V
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Re: Help holding thin material for fly cutting

Post by Harold_V »

3M makes a double sticky masking type tape that will serve your needs perfectly well. It comes papered on one face so it can be handled without damaging the sticky surface. I used to have a couple roles of the stuff, but they died of old age long ago.

If you choose this direction, note that it's very important that the surfaces involved must be free of any oils. If they are not, the tape has the potential to loosen, or may not even grip initially. Using either acetone or alcohol, or, alternately, a basic type cleaner like 409, clean both surfaces well, then apply strips of tape to the table adequate to mount the work piece. It's a good idea to bridge a T slot so you can use it to start the removal process when the cut is finished. Press the work piece in place and tap flat with a soft hammer. The holding quality of the tape is such that error in flatness will be mostly eliminated. If the piece is flipped a few times, which is good practice, there should be no flatness issues when you have finished.

The tape will take a respectable cut, as the forces are not of the lifting type, assuming proper tool geometry. Still, when working on thin pieces, it's wise to take shallow cuts repetitively so the part remains flat. That requires that the part be flipped a few times. To minimize how much you must flip on the tape, get it close by holding in the vise, using the tape process for finishing only. It's a rather slow, but precise method and should yield a part flat and parallel within a thou, assuming the head of your mill is properly dialed in.

You should understand that this method of holding is very reliable if performed properly.

H
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seal killer
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Re: Help holding thin material for fly cutting

Post by seal killer »

Bill and Harold--

I like both ideas. Thank you very much!

Regarding the sticky tape approach: Why not clean a flat piece of material sufficiently larger than my workpiece, then bolt it to the mill table and then sticky tape the workpiece to it?

The surface of my workpiece has a face mill finish now. It is pretty good, but I want to take the visible face milling marks out. I cannot feel them, but I can see them. So I only need to remove a couple of thousandths. I think.

What do you think?

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Bill Shields
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Re: Help holding thin material for fly cutting

Post by Bill Shields »

the tape or superglue cares not if the other surface is the table or not....as long as everything is square to the quill...who cares?

the above posting is one of my uses for 'old glue'..... :mrgreen:
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Harold_V
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Re: Help holding thin material for fly cutting

Post by Harold_V »

seal killer wrote: Thu Feb 02, 2023 6:59 pm Regarding the sticky tape approach: Why not clean a flat piece of material sufficiently larger than my workpiece, then bolt it to the mill table and then sticky tape the workpiece to it?
One of the reasons one uses the tape method is to avoid any obstructions that might limit the cut. For thin objects, there may or may not be clearance for side gripping, and, certainly, any mounting hardware can be an issue unless it is far away from the cut. So then, if the piece you use to bolt to the table is large enough, that may not be an issue, but I suspect it would be. Additionally, unless you have a precision ground plate, you're likely to use a piece that isn't flat, so you end up introducing error that isn't necessary. Even aluminum tooling plate isn't dead parallel (if memory serves, they suggest a one thou tolerance).

Working directly off the table is almost always the best choice. I'm at a loss to understand why you might want to use the plate, but I'm open to your thoughts. Mean time, understand that, to me, the ultimate work surface is the table. Anything else you add is a potential source of error--a weak link, for lack of better description.
The surface of my workpiece has a face mill finish now. It is pretty good, but I want to take the visible face milling marks out. I cannot feel them, but I can see them. So I only need to remove a couple of thousandths. I think.
I understand. How much is required to yield a nice, uniform finish is always questionable. Plate tends to be better than extruded material, but even it has issues. It's a matter of degree. It can suffer from irregularities in thickness. You may find a thou will do the job, or it may take several.

I'm curious. You suggest that there's "face milling marks" on the part now. Mill finishes for this type of material generally are not machined, the exception being aluminum tooling plate, which is Blanchard ground. If you see such marks on your part, it most likely has experienced some machining and is not a mill finish. If I'm wrong, I'd enjoy reading why. I don't claim to know everything. :wink:

H
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seal killer
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Re: Help holding thin material for fly cutting

Post by seal killer »

Harold--

Re: "I'm at a loss to understand why you might want to use the plate, but I'm open to your thoughts."

Not a good idea on my part. Thanks for the sanity check.

The piece with face milling marks is a piece that I face milled rather inexpertly years ago. I am going to use it as the base of a little stationary steam engine.

--Bill
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rmac
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Re: Help holding thin material for fly cutting

Post by rmac »

seal killer wrote: I want to take the visible face milling marks out. I cannot feel them, but I can see them. So I only need to remove a couple of thousandths. I think.
Somebody correct me if I'm wrong, but wouldn't marks you can see but not feel be much shallower than "a couple of thousandths"? Especially in aluminum, would it maybe be easier to remove the marks with abrasive paper?

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hanermo
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Re: Help holding thin material for fly cutting

Post by hanermo »

Make any suitable subtable, so you can epoxy or superglue the part onto it.
Using suitable endstops, like cheap gage pins, or eccentric holders if you can afford them.

The glue will hold the part, unless sometimes it wont.
It´s very uncommon for glue to fail on such large flat parts.

But any programming error on Your part *will* usually cause glue failure due to excess heat.
Pins as stops really lower the risks.
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seal killer
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Re: Help holding thin material for fly cutting

Post by seal killer »

All--

Thanks for all the help! I went with Plan X.

Last night I logged into McMaster-Carr and looked at sticky tape. To be brief, the list wasn't brief. Most of it was foam-backed. I was thinking that was not what I wanted. I am sure some selections were what I wanted, but none of the descriptions said things like 'you can use this to hold a thin piece on your mill for fly cutting if you are fairly courageous.'

Harold (or anyone), if you have more specific guidance on appropriate sticky tape, I'm all ears.

Glue is a neat idea, too . . . thank you, Glenn. Still, I needed to do a job and had no experience with glue, either. That's when I defaulted to something a little more traditional.

My 3/8" x 4" x 5" workpiece has two 10-32 through holes roughly equidistant from the center. I screwed a hefty parallel to the workpiece using those holes and flipped it upside down so the screw heads extended downward. Next, I raised the workpiece and parallel up an inch using 123 blocks. Finally, I used hold down clamping to secure all to the table.

Here are a couple of pictures . . .

Holding thin part-a.jpg
Holding thin part-a.jpg (210.59 KiB) Viewed 1511 times

Holding thin part-b.jpg
Holding thin part-b.jpg (247.61 KiB) Viewed 1511 times
I was careful to get it set up so the cutter cleared the clamping. Next I took a guess at SF/M and decided 586 sounded ok and at 2" of extension (4" diameter), my fly cutter wasn't turning crazy-fast; 560 RPM. It worked well. Here's a very short video . . .

https://youtu.be/YEMuyNCLuDs

--Bill
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Harold_V
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Re: Help holding thin material for fly cutting

Post by Harold_V »

seal killer wrote: Thu Feb 02, 2023 11:17 pm Harold--

Re: "I'm at a loss to understand why you might want to use the plate, but I'm open to your thoughts."

Not a good idea on my part. Thanks for the sanity check.
Well, that depends on the method you choose. For tape, yeah, it's not necessary nor desirable. However, if superglue is your choice, it has a distinct advantage, which I had overlooked. I'm not always right!

H
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