Help holding thin material for fly cutting

[Harold_V]

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?

Depends. If the finish is relatively flat and the irregularities quite shallow, that may be true, but if the irregularities are formed with a radius, what feels smooth to touch can well be several thou. Removing even a thou on a large flat surface is taxing when done by hand and may or may not yield a flat and acceptable surface. A fly cutter has the ability to remove excessive material effortlessly, and, when properly ground, can yield an exceptional finish, something that might be difficult to achieve by hand, especially without edge degradation.

H

[Harold_V]

Congrats on your success, Bill.
The posted pictures verify what I had mentioned previously in the thread about the fly cutter in use. That's extruded material and most likely is not very flat when made. It would feel fine but wouldn't necessarily be uniform in thickness. Hand finishing (the original surface) could prove a daunting task.

By the way, assuming there's no balance issues, you can run the fly cutter much faster, even with HSS. It makes the cut a lot less time consuming and often leads to a better finish. No harm in staying the same speed, either.

H

[Bill Shields]

Particularly with things like brass plate where the minute you take something off one side it turns into a Pringle chip

[rmac]

Depends. If the finish is relatively flat and the irregularities quite shallow, that may be true, but if the irregularities are formed with a radius, what feels smooth to touch can well be several thou. Removing even a thou on a large flat surface is taxing when done by hand and may or may not yield a flat and acceptable surface. A fly cutter has the ability to remove excessive material effortlessly, and, when properly ground, can yield an exceptional finish, something that might be difficult to achieve by hand, especially without edge degradation.

H

Got it. Thanks!

[Harold_V]

Particularly with things like brass plate where the minute you take something off one side it turns into a Pringle chip

A perfect example of internal stresses and how they affect material removal. Brass is usually work hardened and loaded with stress because it's rolled cold. The hardness designation (like half hard) reveals the degree of cold working.

H

[Richard_W]

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.


--Bill

I go to any store that sells carpet tape. It's double sided and has worked well for me over the years.


Richard W.

[seal killer]

Richard--

Thank you!

--Bill

[Harold_V]

Bill,
Sorry for the delayed response. It's been years since I had any of that tape and I didn't record the product number. That said, I've done some snooping and think I've found what is the same product I used to use. If nothing else, the description matches exactly.

One thing I've noticed is that these tapes are really expensive. This one tends to go against that trend, so I've ordered a roll for myself. I'm willing to gamble on it for that reasonable price (about $18 with taxes). If you'd care to investigate, here's a link: https://www.ebay.com/itm/295143658604?h ... R4LjtYXEYQ

I have been aware of the use of carpet tape, but the one thing I don't like about it is it's very thick. That allows for miniscule movement of a part when being machined, which, in turn, can lead to failure. I'm not suggesting that it doesn't work---just that it most likely offers risk where it can be avoided. That would be particularly bad for a tall piece that might be inclined to tip sideways under the cut.

I learned about holding by tape when one of the components of the brake system for the Sergeant Missile couldn't be held without distortion. It had an exceedingly tight tolerance, a large truss type magnesium casting. As a last resort they turned to taping it to the table of the machine, which yielded acceptable results. That was even though the cut was taken several inches above the gripping point. It works, and very well, assuming one cleans the surfaces properly.

H

[seal killer]

Harold--

Thank you for the link!

--Bill

[seal killer]

Harold--

I've got a 36 yard roll coming in from Amazon. I read some of the reviews. Woodworkers rave about its ability to hold down workpieces.

I'll (eventually) report back.

Thanks, again.

--BIll

[Harold_V]

I don't have a clue when I'll try the roll I've ordered, but I'll try to remember to comment when I do. After ordering I noticed the same seller offered it in 1" width for a lower price, which I would have ordered instead, but it's easy enough to split in widths that are acceptable for one's needs, so no problem.

The rigid backing that accompanies the tape is important. If it is stretched when applied, it won't hold well. I used to clean the mill table, then apply a strip as required, never shorter than the workpiece, often more than one, side by side, and always bridging a T slot, so the work piece could be removed without effort. Once the required strips were in place, using a scriber, I'd start separating each of the backing strips, which act as a barrier so the tape doesn't stick to itself on the roll. I wouldn't remove the strips, just start each one at a corner so they'd be easy to grab when I was ready to apply the workpiece.

That done, the next thing I'd do is to clean the workpiece well and ensure that it was dry. Pull off the protective strips from the created pad of tape on the mill table and apply the workpiece. Tap it down with a soft hammer and you're good to go.

It should be noted that this tape readily releases with a hydrocarbon solvent. However, due to its ability to grip tightly, one can still apply a film of lubricant to a fly cut so chip welding isn't a problem. The solvent penetrates the tape at an exceedingly slow rate due to the intimate contact, so the cut is usually over long before there's any degradation of its gripping power.

H

[seal killer]

Harold--

Great details. Thank you again!

--Bill