New Machine Build- Building new machine - questions

[philba]

I am building a CNC router and like the simplicity of the jgro design and the advances of the Joe2006 design. However, I don't have access to a CNC machine so the joe2006 design is out of reach, for now. I expect to use this first machine to build a second machine more along the lines of joe2006.

I have a decent workshop: table saw, sliding compound miter, 14" bandsaw, drill press. I also have a very small mill and lathe (Sherline that I picked up at an auction when no one else bid). I would categorize my wood working skills as good but not great. My metal working skills, well, I'm learning...

Anyway, I've been playing around with a design that is fairly similar to jgro and incorporates some of the advances of joe2006. In particular, wider use of torsion boxes and Y/gantry bearings on the outside. I didn't go for a quad rail design as I think that requires more precision than I am up to for now. I've included 2 pictures. Most of the material is 1/2" MDF with 3/4" in a few places. The Z axis assembly is pure jgro. 1" pipe rails for Y and 3/4 for the other two axises - just like jgro. I'll probably use acme 1/2"-10 leadscrews and traditional antibacklash nuts from hdpe/delrin. Not all the fastener holes are in the current design, I'll detail that out when I get closer to final design.

What I'm looking for are any comments on problems to watch out for and suggestions for improvement. I'm concerned that the gantry might be too heavy for the rails. The unsupported rail length is 40.5".

I'm not worried about the electronics and software - I've got that covered.

Thanks in advance
Phil

[philba]

Here's another view of the gantry showing how the torsion boxes are used. Dimensions are 21.5H x 35W x 9D (at the top).

[ger21]

Without supporting the pipes, the torsion boxes won't make a lot of difference, as you'll still get a lot of flex. By using jigs, like a table saw cutoff sled, and a drill pres fence with stops, you should be able to build the parts for the Joe 2006. For duplicate parts, make one good template, and use a router with straight bearing bits to trim them all to the template. If you mark them all so the orientation is the same, you should be able to build a very straight machine, with the rails being parallel to each other.

And I'd recommend 1/2-8 2 start acme, and DumpsterCNC nuts.

[philba]

Thanks! I have read several comments, including from Joe, that said it would be hard (if not impossible) to build a joe2006 machine with out a CNC router.

I had thought about using a router with templates but the comments dissuaded me. Do you know of any one who has does so? My biggest concern is repeatability of a manual process.

[mvaughn]

Take a look at this build:

http://cnczone.com/forums/showthread.php?t=31436

He used templates to accurately make duplicate parts.

[philba]

I like that design - I can see how I could use a router table to cut the groove for the rail and keep it within a reasonable tolerance.

Thanks.

[stef_d]

After building my first machine a few months ago, i will not go for unsuported rails again.
there are alternatives to those, which are definitely worth investigating.
flex is a major issue with cnc, as you fill find.