I have a small part I need to modify slightly. It is steel, but with a polished finish, and I don't want to scratch it up. It's difficult to tell, but it may have a very thin epoxy or some other protective coating. It's hard (RC ~ 52), and I will be using a sharp carbide end mill and light cuts. I only need to remove 5 to 10 mils in one area.
I don't want it to slip in the vise, and I'm wondering what's the best way to hang onto it while protecting the finish. I could use tape, but Scotch tape is a bit slippery, and the adhesive on masking tape is thick enough I'm concerened it might creep. I could ue thin cardboard shims, or maybe even aluminum, but that might mar the finish.
I keep a box of those nice hardwood Jenga blocks in the shop for this type of thing.
I always buy the grandkids a set of Jenga blocks for Christmas and, of course, they get tired of them soon and leave them here at Grandpas for use in the shop. They are very handy for many jobs.
You could use leather shims to clamp the part. I have done this more than once. You can also buy these low temp melting plastic pellets that are made to be used to make custom holding devices, such as handles for files that fit your own hand perfectly. I had many custom arm braces made from this type of plastic over a two year period during wrist reconstruction surgeries. As the swelling would go down just warming up the braces with steam would allow them to be reformed to a perfect fit. When the plastic cools on something it sticks pretty well to it but when warm comes off. Eric
For very light cuts in soft material I have used double-back tape to "glue" parts to the table. Although it is not a cure-all it does work if the cuts are light and there is sufficient area to "glue" down.
I do the same, but with hardwood such as maple, cut on a band saw to more-or-less fit the part, and finished by hand to a reasonably-good fit - doesn't have to be perfect. A quick spritz with spray adhesive sometimes adds a little friction.
I would use cardboard about the thickness of cereal box cardboard (or shirt cardboard from the cleaners, if they still stuff shirts with that after cleaning and ironing. We've used a washing machine at home since about 1976, so I would not know. :-)
Anyway -- the cardboard is just thick enough so it deforms into any surface irregularities -- in the vise jaws and in the workpiece, and is a very good protection against slipping. If the surface of the workpiece is too good, the only deformation of the cardboard will be around the edges.
Just one use per piece of cardboard. Soaking the cardboard with oil might make it a little softer and thus deform better -- but it may attack the postulated coating.
Single 'l' not double. That is common in some trades e.g. dimensions in data sheets for intergrated circuit pin spacing) as a substitute for "thousandths of an inch". The typical DIP package for TTL logic was 300 Mils (0.300") and the pin spacing was 100 Mils (0.100").
"Mils" as in "Mili-Inch".
O.K. Checking a recent data sheet from TI for the TLV2474 and its brothers (OP-AMPs) shows that they now give dimensions in decimal fractions of an inch (and in mm).
Before this turned into a pleasant "pick on Gunner" session, you were askin g about how to grip your shiny part in a vice. Assuming that it has flat si des to bear against the vice jaws, I might try some contact cement, applied very sparingly, Perhaps to only one surface - not to glue the part to the vice. You could use something like 3M 77 spray mount adhesive. Holds like t he Dickens, but is very thin. It'll clean up easily with solvent.
You might also try rolling paper. It's incredibly thin but still pretty tou gh. You might try gluing that to either the vice jaw or the workpiece.
Pete Keillor wrote in news: snipped-for-privacy@4ax.com:
I used this approach. It gave me a good grip, and didn't scratch the part. That's the good news. Either the part is a lot harder than they claimed, my carbide is softer, or (more likely), my little Clausing mill isn't rigid enough to make small cuts in hardened material.
I haven't figured out what was flexing or slipping (the end mill in the collet is another possibility), but the end mil barely scratched the surface. I finally ended up grinding it down freehand with a Dremel. It isn't as pretty as I would like, but it worked.
Sorry about the firestorm about "mills". The spare "l" was a typo on my part. I have worked in the aerospace electronics arena since the early
70's, and was taught machining by a friend's father with a similar background.
"Mil" is a VERY common term in microwave circuit work, electronics, and printed circuit design. All the machinists I've talked to (in & out of that field) in the Boston area recognize it. I also worked at HP in silicon valley in the early 80's, and no one there had any issues with it, so I don't think it's regional. It may be that if you do metalwork for the electronics industry, it's a common term. I can see where large manufacturing outfits that generally deal with bigger dimensions might not use it as much. I just find it easier to say & type than "thou". Verbally, "thou" works well, but when typed, I start wondering when "thee" is going to join the fray.
I just raised the table of my Clausing with a chucked rod bearing down on a load cell in the vise. Between the two the deflection rate is almost 0.005" per hundred pounds. The load cell compresses ~0.005" per thousand Lbs in the milling vise, so most of the flex is in the mill. The measurements started at a 200 Lb preload to remove zero errors.
Both the knee dial and load cell returned to zero simultaneously, showing that the collet held the rod without slipping. 1200 Lbs of clamping force requires a little less than the max vise handle pressure I apply.
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