Replies to This Discussion

Permalink Reply by Emin Bu on May 27, 2012 at 10:56am

maybe something like this http://solsylva.com/cnc/rack_pinion.shtml

Permalink Reply by Emin Bu on May 27, 2012 at 11:02am

http://www.techno-isel.com/tic/Catdas/Gantry3.htm very useful link with good components

Permalink Reply by Kevin Bouchard on May 27, 2012 at 11:31am

I'm in the dark as to what kind of parts should be designed first, but if you can throw together a couple of sketches I can start modeling.

Permalink Reply by Kevin Bouchard on May 27, 2012 at 6:11pm

Am I doing this right?

http://www.diydrones.com/photo/albums/diydrones-cnc-prototype

Permalink Reply by Fabien Bruning on May 28, 2012 at 3:43am

There's a great concept for  a statically determined linear slide in this document, Figure 6a. http://alexandria.tue.nl/repository/freearticles/605520.pdf Unfortunately the document is in Dutch, but I didn't want to "steal" their drawing.

The basic idea is that you want to fix a cart in five degrees of freedom, which you do with five roller (skate?) bearings. The four on the left and the one on top on the right. The two bearings on the bottom are mounted on a rather thin plate, so that they push the other five onto the guide.

This means the straightness of the cart is only derived from the left tube, you could even position the second tube a few degrees off without any harm done.

Permalink Reply by Fabien Bruning on May 28, 2012 at 9:28am

Hm, I haven't calculated it but you're right that straightness was the first thing I was going for. I wonder if those eBay dovetails are any good.

Permalink Reply by Fabien Bruning on May 28, 2012 at 10:43am

That's a very generous offer, unfortunately I can't seem to find the Hong Kong new ones, they only have linear ball bearings. (I assume you mean those slide bearings in dovetail shape right?)

DistributorPermalink Reply by Dany Thivierge on May 28, 2012 at 7:43pm

Again I had to educate myself... had to search for  these dovetails to follow the conversation... 

found this: 

http://www.iqsdirectory.com/linear-slides/dovetail-slides/

now I know what they are! :) 

Permalink Reply by Kevin Bouchard on May 30, 2012 at 2:08pm

Added new drawings and comments to the album:

http://www.diydrones.com/photo/albums/diydrones-cnc-prototype

Permalink Reply by Kevin Bouchard on May 31, 2012 at 8:07pm

Good. I can do more CAD on the weekend.

Just tell me if you need any of the orthogonal drawings.

Permalink Reply by Kevin Bouchard on June 3, 2012 at 2:08pm

Can you give me dimension pointers?

- What diameter screws?

Barring any, I'll make the blocks 3/8 in thick, proportionally wide and 5 in long. Should be done in an hour or 2.

Permalink Reply by Kevin Bouchard on June 3, 2012 at 2:35pm

Good. If you have anything else, throw it my way! I have some time off tonight and CAD is pretty relaxing to me :p

There's one thing I don't get though... you want to squeeze the gib with those 7/32 screws, but the pressure is all going to be on the corner of the screws, no? Unless you're thinking about making notches in the gib, or something else...

Pardon me if some questions are stupid, but I've only *used* milling machines in the past (and not extensively at that), not *designed* them :p I'm reading up on the topic but as you said, there's not an incredible amount of information sharing among machinists ;)

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