Anyone have opinions on Cratex products?

[John Hasler]

If this were my project, then, after cutting the acme threads, and using this pic as an example, I'd probably setup my mini toolpost grinder like this, and make 'thread cutting' polishing passes inside the nut, concentrating on the thrust side of the threads. Could use a V-edged wheel, or trim/dress a cylindrical wheel, and/or tilt the grinder to match the pitch angle of the acme thread. Or, look into the softer, more-compliant G-flex wheels mentioned by holescreek above.


As far as the colors and grit sizes go, I'm not quite sure how to answer that. Yes, these wheels have a grit of particular sizes, but the results don't really match what you'd get with sandpapers and such. Almost like a world of its own. Takes a bit of playtime to get the feel of the various grades, and how they work on different materials. This pic shows my results with the Craytex 'medium' grit on an ER32 collet. It's not a mirror finish, intentionally, because I wanted it that way.

I was thinking of putting one of the Craftex sticks in the boring bar and going over the threads with it, but I may try your idea. Looks like the medium would work for me. I don't need a mirror finish, but realistically I know that my threads are going to have enough burrs and roughness to impact efficiency.

 

[Andre]

Those "cratex" sticks are used a lot by gunsmiths to jewel rifle bolts and such.


http://www.customjewelshop.com/rifles/1ingunm77.jpg

 

[Holescreek]

I was thinking of putting one of the Craftex sticks in the boring bar and going over the threads with it, but I may try your idea. Looks like the medium would work for me. I don't need a mirror finish, but realistically I know that my threads are going to have enough burrs and roughness to impact efficiency.

I've never made an acme nut, wouldn't it normally be lapped?

 

[george wilson]

There are much better made products than Craytex. They are an old,well known product. But try looking at Rio Grande or Gesswein for more advanced abrasive wheels.

 

[John Hasler]

I've never made an acme nut, wouldn't it normally be lapped?

I intend to lap, but this is a bit of an oddball application. There is no leadscrew. The nut threads onto the threaded ends of a .375"X1.00"X2" bar that fits into the drift slot in the spindle of my mill. The nut drives it up and down in the slot and it moves the MT3 collets by way of a short drawbar. I'm concerned that enough lapping to smooth out the nut will wear the ends of the bar down too far since the area there is so small.

 

[rgray]

I used to use these for shinning up 2 stroke cylinder ports. Used the green and brown. They do a decent job on the aluminum. They wear out pretty fast. The mandrels to spin them on used to strip out on me. The cratex would spin on the mandrel at times and after while it would smooth it to where it didn't hold anymore.
I got more use out of a 3" sheet rock screw cut off it fit in the 1/8 collet for the fordom tool holders. Worn pieces of cratex were threaded on down the screw when a new one was installed. That way covering exposed threads so they didn't hit and damage the part behind the work area.
The max rpm on the fordom was 15,000. They worked best somewhere around 1/2 of that. I had a foot pedel so I can't say a speed but I know I didn't go wide open with cratex much.

 

[Hannadog]

I have an assortment pack of coarse, medium, fine, extra fine that I used for gunsmithing. They seem to work best around 1000-1100 RPM in the Dremel I use. They're not cheap but they work great for polishing. Really produce a smooth surface without grinding away metal.Small enough for most of my work.