dovetail guides without grinding finish?

[medved]

Hello

I have a question about making of dovetail guides.
I found small manufacturer with professional cnc machine which can mill objects up to size 1m x 0.6m.
When I asked him, he told me he can easily make dovetail guides.
The problem I see is, that he can make dovetails with cutter, but he doesnt have a grinder.

My question is, can dovetail guides be made functional without final finish with grinder?
The cuts made on this machine are wery clean, surface on aluminum is allmost mirror alike.
I believe it would cost me alot to get rails to some company specialized for ACCURATE grinding of big objects.

thanks for any info on this subject

[Mcgyver]

what are you making them out of and what’s the application? ideally dovetails are not ground as there is not where for the oil to go. hand fitting via scraping is best and the scraped surface leaves a surface with micro pockets for oil to reside. its my understanding that commercial ones, that must be ground because the part is hardened, use a scraped mating piece so that it can stay properly lubricated.

a dovetail is a bearing surface, just like a plain bearing. This is a simplification, but basically the key to a bearing is riding on a film of lubrication not how hard or smooth the bearing is.

[medved]

Originally Posted by Mcgyver what are you making them out of and what’s the application?

Well for now this are just considerations for distant future project. I saw oppurtunity to get long dovetail guides precisely manufactured for only a fraction of cost of used linear bearings(like thk), so I thought it is worth trying.(what is more, one dovetail guide is worth TWO linear bearings, allready perfectly prallel aligned)

Dovetail guides would be made of iron because of its good ability to capture oil film.
They would be used on very big mill, built from scratch(as I said, distant future fantasy).
My fear was, that if dovetail surface is not completely free of traces of ROTATING cutter, there is a possibility for a guide to get blocked, or for friction to increase, or small morsels could break away from sliding surface and consequently destroy it.

Originally Posted by Mcgyver hand fitting via scraping is best and the scraped surface leaves a surface with micro pockets for oil to reside.

Im not sure what scraping technique means -I imagine it is a knife that makes long linear moves(and is not rotating). Mine dovetail guides would be made with ROTATING "dovetail milling cutter".

So my question is, can dovetail guides be made, is it common practice to be made with dovetail rotating cutter, without also being precisely ground?
Can they be "grund" by hand using grinding paper - without danger of destroying slides?


thanks

[Mcgyver]

I think the answer is yes, dovetails are frequently done without grinding. Intuitively the dovetail seems a better way (pun intended) than linear bearings as it has a much larger bearing surface, but I lack experience with industrial cnc machines to really know if this is an issue.

there's a bunch of content here on scraping that a search will turn up. here's some pics i took on the subject Way lapping, Scraping, Gib adjustment and Lock screws