Lead screw supportquestion

[nakchak]

Im designing at the moment a leight weight low cost 3axis router/engraver, i have pretty much sorted the design in my head for the axis movement, i am how ever stuck upon how to drive each axis. From a little bit of deduction and a lot of trawls through the posts here ive managed to narrow my choice of lead screw support bearing assemblies down to 3 choices. Id like as much feed back as possible for my choices, TIA.

Rough Spec.
Cheap as possible
simple to build as possible using easily obtained parts in the uk
as little machining as possible

With that in mind ive ruled out turning my threaded rod to a non threaded profile for my bearings to make contact with, and would like to use less than two bearings per end of the lead screw, (this is a prototype machine and if i feel that i can improve it by altering bearings at a later date i will, but for the time being its all about making as high a preforming machine as possible, as simply and cheaply as i can)

As ive stated before ive pretty much narrowed my choices down to 3, so if you could vote and comment on my 3 sketches (lead_screw_support_bearings.gif) it would be much appreciated
Heres a quick breakdown of the design :

Design A

• Flanged bearing
• Bearing interfearence fit into mdf
• End nut loctite'd on

Design B

• 4 Screws holding washer down
• Adjustable??/Misalignment forgiving

Design C

• Bearing interfearence fit

[Mr.Chips]

It looks like you plan on putting a bearing on the motor end. thisn't isn't absolutely necessary as the motor bearings can be the bearings for the motor end. You only need bearings for the other end. This simplifies things. Lot's of people use this method.

Hager

[buscht]

I used bearings on both ends. Here is a picture of the end nearest to the motor. Its very cost effective and simple. The rollerblade bearings are cheap and since they are deep groove they work well for thrust.

I counterbored the MDF the same diameter as the bearings and just pressed them in. I just shot a couple of screws in tight next to the bearings and used the heads to hold the bearings in place. Real simple, yet effective.

I prefer to make the mounting block adjustable, not the bearing in the block.

[ger21]

Originally Posted by Mr.Chips It looks like you plan on putting a bearing on the motor end. thisn't isn't absolutely necessary as the motor bearings can be the bearings for the motor end. You only need bearings for the other end. This simplifies things. Lot's of people use this method. Hager

If you plan on using the motor to handle the thrust loads, that's not really a good idea. The bearings in steppers are not designed to handle thrust loads. It will probably be OK for light work (balsa) , but for any medium to heavy work you should have thrust bearings on the screws.

[Mr.Chips]

Sorry I guess I didn't explaing my posting enough. The other end, not motor end had a thrust bearing on my machine. I was going to have bearings on both ends but BalsaMan said he only used bearings on one end, and cut MDF and aluminum on his first machine.
It's true two bearings are better than one. Was thinking of your cheaper, simpler comment.

[ger21]

As long as you have a thrust bearing at the other end, you should be OK then.

[ViperTX]

When you say "cheap" do you mean inexpensive and accurate to some measurable amount?
How much variation can you live with?
Zero-backlash nuts, the precision of the ballscrew if you're using one and the backlash due to how the screw is mounted...these are all critical in your decisions....well of course cost is a consideration.