Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.
Heat as mentioned will get CA glue to release, something important to remember though is most or maybe all? CA glues give off fairly toxic fumes when heated to that release point. https://www.stewmac.com/How-To/Online_R ... sives.html
CA work holding is even used in industry for hard to hold parts. It's an idea borrowed and modified from the watch makers bag of tricks and there much slower to use "shellac" pot chucks for part holding. CA or even epoxy glues work, but there brittle and don't like high shock loads such as interrupted cuts or the heat from cutting that could go high enough to reduce the bond strength up to getting the part to release. Double faced tape similar to carpet tape is also some times used even for milling. Proper industrial rated double faced tape is normally used since it's holding power is far greater than any off the shelf carpet tape at a big box store. https://www.tormach.com/blog/workholdin ... ided-tape/ I've used the idea a few times to polish thin parts held to a lathe face plate, but again you have to watch just how hot the part is getting. Don't ask how I know that.
Ever breathed the fumes from hot CA just once? My reaction says it's highly toxic. There's enough other Google hits about heated CA glue being a real health issue I'd not take the link I posted too serious even if he say's he's a chemist. But I should have actually read all of what was in that link before I posted it. For that I apologize.
Older CA glues give off cyanide gas on curing!! CA = "Cyano-Acrilate."
Years ago I ended up in the hospital ER as a result of this, and my sinuses remained swollen closed for several days post exposure. Very nasty.
That's when I changed to "Odorless CA" glues. I remain badly allergic to the gaseous CA glues.
I was going to use super glue to hold some small parts for milling, but due to the responses here of toxicity and heat needed to release the parts, I was wondering if using "VHB", Scotch double stick tape would work as well. I have used it previously, but limited cutter feed to very light and that was on aluminum. I want to mill brass parts which may require more cutting force. I guess I should try a sample cut and see if it works.
The issue with using super glue is it takes 24 hours for a full cure (unless an accelerator is used) and the toxicity and release issues.
Most cyanolacrylates reach well over half their ultimate strenght in 10 minutes. No need to wait 24 hours. They do not release cyanide. Some people are allergic to the fumes but most just find them noxious. I'm allergic to bananas but I don't claim they're toxic.
I've used double-sided tape. It works but it isn't very strong. Cyanoacrylate is good for about 2000 psi after 10 minutes, according to the literature.
Plus there's double side tape from a big box store and the same from an industrial supplier. There NOT the same thing. Much more money for the actual industrial rated version, but 3 or more times the holding power. 3M etc have a lot of user information about those products on there web sites. https://www.3m.com/3M/en_US/bonding-and ... ed-tape/An old wood turning trick that can also be used with CA glue is to bond the part with a piece of paper between the part and whatever surface your bonding it to. The bond is still almost full strength but the paper leaves a weak spot that can be split using an old but sharp chisel between the surface and your part. It still depends on the part shape and it's cross section strength though. Thin weak areas can bend so acetone or other solvent would need to be used.
I haven't tried double sided tape at all. A friend suggested, and I've seen it on Youtube, putting painters tape on the part and the fixture and then applying the glue to that. The idea is that when done, you knock the part loose and the tape just peels off. It was pretty chilly in the garage when I was making this part, so I was afraid that the tape wouldn't stick well. When I put it on the part, it peeled off very easily.
The superglue sat for only about 10 minutes before I started making passes. I didn't have to remove a ton of material, but I wasn't taking super light cuts either, and it held just fine. The removal process that I went through should be proof that it held more than strongly enough. Of course, I was worried it would break loose, so I applied glue over the whole mating surface. Knowing what I know now, I would probably just use a few drops around the perimeter.
If you aren't working in a cold environment, the tape/glue combo might hold plenty well for your parts. Or if they aren't too delicate to knock free, the glue alone might work.
One advantage of the glue is that the layer is very thin and quite rigid. A layer of tape will be slightly flexible and so might cost you a bit of precision.
I'll try the tape-glue-tape system some time. Sounds much more convenient than have to soak or cook the glue off.
The double stick tape I was referring to isn't really a tape, but a film made by 3M called VHB (very high bond). It is .002" thick and also known as "glue on a roll". It is used to replace rivets on sheet metal panels, like on semi truck trailers. As I said previously, I've used it to hold aluminum for milling, but I was taking very light cuts. Brass is harder and VHB may not be strong enough to hold it for milling, but I will give it a try and let you know how well it works.
Mr Ron wrote: ↑Fri Jan 24, 2020 2:01 pm
The double stick tape I was referring to isn't really a tape, but a film made by 3M called VHB (very high bond). It is .002" thick and also known as "glue on a roll". It is used to replace rivets on sheet metal panels, like on semi truck trailers. As I said previously, I've used it to hold aluminum for milling, but I was taking very light cuts. Brass is harder and VHB may not be strong enough to hold it for milling, but I will give it a try and let you know how well it works.
UPDATE:
I tried super glue to hold brass to aluminum while drilling holes in the brass in the mill. All the holes were drilled using a #41 drill. While drilling the last 2 holes of 24 holes, the glue interface let go, breaking the drill bit. I reset the piece this time using Scotch VHB film, but haven't tried milling yet. The two surfaces were clean and flat, so the bond should have been good. The glue was applied in "dabs", not a full coverage. I don't know if that would make a difference.
