I need your thoughts on using 3 linear bearing for the Y axis cnc router

[rodjava]

If I were to use only 3 linear bearing for my Y axis, what would be the best configuration? One on top, two on bottom? Or vise versa. I can't think of a reason why one is better than the other.

I only have 3 linear bearings which rules out other options.

BTW, I'm building a Data cut hybrid.

Thank you in advance.

Rod
San Francisco

[LeeWay]

It might depend on your Z axis design, but like you have them looks good to me.
It might make a difference with twisting forces while cutting, so I would say that the way you have them is the most logical.

[Oldmanandhistoy]

Originally Posted by LeeWay It might depend on your Z axis design, but like you have them looks good to me. It might make a difference with twisting forces while cutting, so I would say that the way you have them is the most logical.

Totally agree

[Geof]

The most important thing is keep the two that are on the same rail as widely separated as possible. Make sure that when your Y axis travels full distance each direction that the bearings trucks do reach the end of the ways.

[Switcher]

The way you have them setup, looks good to me, also.

.

[rodjava]

Thank you to everybody who responded.

I'll keep it like it's pictured. I thought that there was some type of mysterious force to consider. I don't have to worry about flex because of the 25mm bearings and all the 1" A/L which makes up the gantry.

Rod

[Oldmanandhistoy]

Originally Posted by Geof The most important thing is keep the two that are on the same rail as widely separated as possible.

A very good point to keep in mind; have you worked out your Z axis lay out?

These bearing systems can take very large loads and guessing the size of those rails and trucks from the picture they would probable be more ridged than you need, unless you are doing some seriously heavy cutting. So IMHO having the bottom trucks almost touching will be fine to maximise Y axis movement.

What do you other guys think?

What are you planning to cut, how heavy do you want to cut and what spindle do you plan to use?

If you are confident with your Y and Z design please just ignore this post

[rodjava]

Here is pic of my gantry. Made mostly of 1" thick tool plate A/L. I'm building it to cut mostly A/L and mild steel. It's a data cut cnc router design which I "Pimped out"

THK HSR 35 rails and bearings for the X. THK HSR 25 rails and bearing for the Y & Z. Precision rolled 25mm ball screws for both X & Y and 15mm precision ground screws for the Z. Actual cutting area is 28"x48"

This is a picture before I machined and installed the Y ball screw. I had to add 1" risers to the Y rails to accommodate the large 25mm screws and the block mounted to the nut.



This a picture after the mod. I still have to machine the Z screws down to size and install them on the 1" plate the spindle will mount to.

[Cartierusm]

Hey how's it going. This is Carter, we emailed each other back and forth from Craigslist a while ago. Looks like yours is coming along. I got mine finished about 6 months ago, it's wicked fun. Let me know if you need any help. I can make parts on my CNC or my bridgeport.

[rodjava]

Carter,
Good to hear from you.
My build is taking a while. 75% completed. Still have to search for servos and then the electronics.

Where did you say you live? I'm in the city. When it comes to the electronics, I'm a little lost. Might need your help then.

Building is no problem. I have a BP too.

Rod

[Oldmanandhistoy]

Aluminium and mild steel, that’s some serious work you have planned, will be interested to see how she performs once complete. Obviously the ballscrews and linear rails are up to the intended task so it will come down the rigidity of machine frame.

Wish I had a BP

[Cartierusm]

Oldman, if you have the space it's really not that big of a deal if you have patients. Most BP go for $3000 and up but every single day companies and people moving let them go for $1000. If you have the cash ready you should be able to pick one up. Just be patient. Depending on where you live there are a lot of companies who sell them on Ebay and craigslist. Opps I just realized you are one of those british folks...I love London, where are you located?

Rod, I'm in Burlingame. No problem if you need help just ask PM if you want my phone number. The electronics at first were a big problem deciphering all the crap, especially since I didn't know what step and dir were, but now it's actually very simple, very hard to screw up if you know what you're doing. I have a lot of experience at mods and upgrades as I had a hell of a time with Keling.