[aquaveg]

Hi all i am very new to cnc and have started building my own machine have been building for about two months have got most of the hardware side of it done almost up to electrical my problem is the linear bearings which are sbr16uu purchased on eBay ,they do not seem to run smooth i have packed them with grease for lubrication but they run very jittery and on the x axis the bearing are jamming up which could be a load problem as the unit is all built from steel so is heavy but did not have this problem before i packed the bearings with grease. any help or ideas greatly appreciated thanks.

Have built is so far with no plans just from pics of the net sort of designing as i go.

[vtx1029]

Loosen one or both of the rails on the X axis. The rails could either be not aligned or your base that the linear rails are bolted to are not straight. Did you surface the rails the linear slides are bolted to or do some sort of epoxy leveling?

[rowbare]

The bearing blocks on the X axis seem to be pretty close together. This makes it more susceptible to racking. Maybe that is the issue?

bob

[amishx64]

I definitely did not mix up the axies. Nope. Nothing to see here folks. Move along. :wave:

[ger21]

Or maybe I am the one confused...

Yes, you are. (chair)

Most people consider the axis along the gantry as the Y axis. The gantry travels along the X axis, which is usually the longest axis.

[ger21]

If the bearings are tight, the slightest misalignment will cause binding. You didn't say if it was one axis, or all of them?

[amishx64]

Yes, you are. (chair)

Most people consider the axis along the gantry as the Y axis. The gantry travels along the X axis, which is usually the longest axis.

Oh snap! That's what I thought a long time ago then I saw it explained somewhere on the zone as I just said and now I'm back to where I started.

We'll I'll edit that out and pretend like it never happened. Hopefully no one else gets confused. (chair)

[ger21]

There's plenty of confusion already. Some machines do label the axis as you do (did?), the Joes 4x4 hybrid being a popular one. I believe Joe does it that way because he stands facing the gantry, where as I stand on the side of my machine.

[aquaveg]

Thanks for the replies, the axis that i was talking about was the longest running the length of the bench was not sure if this was x or y .

The other axis did also become a lot harder to move once i added grease to them,Should i be greasing the bearings or just using an oil or other lubricant regularly?.

I am also thinking of adding two more bearings to each side on the x axis (long side) to help spread the weight hoping this will help as the unit is a little high i was thinking this would help.

[crob09]

Each axis should have 4 bearings.
You can obtain Pre-loaded linear bearings but gennerally the DIY mill will not use them because of cost and beacuse the accuracy is not needed.
The bearings your using may not require grease, generally they don't if they are roller bearings.
If your having issues it could be becuase your out a little on one end, if your rails are out just a fraction your resistance will increase big time! 1/32 on one end can equate to inches on the other, the bearing will take up some slack.
If your overloading due to binding you will hear noise, also by greasing things your taking up even more slack hence why things get tighter when you pack the bearings.
I would recalibrate your shafts or rails (whatever you have chosen to use).

[rockcliff]

I think once you get both sides actually powered up and the screws attached, you should see some better results, as the gantry will be driven evenly, I have built many sliding type machines and devices from steel, and this is a common thing to have this walking when moving the slides manually by hand on a wide frame spacing.

Linear bearings have very little give, and with a welded steel frame like you have made , without machining the faces flat, you would have to shim some bearings and or rails to get them into better alignment.

if I was going to change anything on your machine I would consider widening the bearing spacing, but wait and see how the slides move once it's powered with 2 screws,

[crob09]

The problem with having two screws is control, I tried it once and ran into problems slaving one motor using Mach3.
It will fix any walking issues but really consider another solution, the best bet is to have preloaded bearings and rails for the one axis. The "LAH" series and rails will prevent any movement, and they are pre-loaded so your tolerance is closer equating to more precise movement.

[ger21]

The problem with having two screws is control, I tried it once and ran into problems slaving one motor using Mach3.

Probably 95% of the machines you see being built here used slaved motors and Mach3, and they all work fine. There are thousands of mach3 users using slaved motors with no problems.

Using slaved motors to move a gantry is the easiest way to get a rigid gantry that doesn't rack and bind.

[aquaveg]

Thanks for all the help
I am going to check alignment and I am also going to widen the bearings on axis X so that it has a bigger foot print as it is top heavy and i think this is the main problem.