noobie

[HiltonSteve]

I doubt you will be able to run from the center, even with a stiffer machine using profiled rail can crab, and you are using MDF and this will cause you big problems.
Even running the screw through the center will still casue you problems.

Have to agree with Gary here, using open bearings will always cause you crabbing problems which is why I dismissed them for my design, but driving from both sides will soon sort that out.

Though, I have built up my X axis gantry yesterday on my machine which has a bed size of 1000mm x 600mm and using 20mm THK linear bearings gets virtually no crabbing, I will be driving this machine from the centre. It is a pretty solid all aluminium machine which does help though. will get a clock gauge on it later to measure it but it is not a lot.

Gary - Don't forget to send me those 16mm ballnuts when they come in, they are the only piece missing now before I can get up and running.

[Gary]

The ball nuts leave the factory on the 20th so i expect them to arrive mid week (Wednesday / Thursday.)

Have to agree with Gary here, using open bearings will always cause you crabbing problems which is why I dismissed them for my design, but driving from both sides will soon sort that out.

Though, I have built up my X axis gantry yesterday on my machine which has a bed size of 1000mm x 600mm and using 20mm THK linear bearings gets virtually no crabbing, I will be driving this machine from the centre. It is a pretty solid all aluminium machine which does help though. will get a clock gauge on it later to measure it but it is not a lot.

Gary - Don't forget to send me those 16mm ballnuts when they come in, they are the only piece missing now before I can get up and running.

[HiltonSteve]

The ball nuts leave the factory on the 20th so i expect them to arrive mid week (Wednesday / Thursday.)

Nice one!

May be up and running by next weekend then.

[jonm]

thanks for the input guys , may bin the mdf idea seen aluminium herehttp://www.aluminium-profile.co.uk/a...10mm_Slot.html

could get a frame for about £60 ,would it crab with 2 bearings per rail spaced say 200mm , could i run two skate bearings against the outside of the frame on the non driven side to keep it parallel and stop the racking , i have aready ordered the 16mm rails from zapp

[HiltonSteve]

I would still say drive it from both sides, just get another motor and trapazoidal screw and it will be a much better solution. It may cost you a little bit more but at least you know it will be right!

Just wire both motors to the same driver card, so you won't need to spend more on electronics.

[Gary]

I dont suggest connecting both motors to the same driver.
This can cause problems with the driver and will also void the warrantee of the driver.
As an example of the problems you will see is that if the driver has any anti resonance circuitry this will most likely cause this to not function as expected.
You will also have issues with BEMF.

I would still say drive it from both sides, just get another motor and trapazoidal screw and it will be a much better solution. It may cost you a little bit more but at least you know it will be right!

Just wire both motors to the same driver card, so you won't need to spend more on electronics.

[jonm]

thanks hilton steve
will gladly take your advice and go for twin screws , i dont want to waste time and money and end up with a machine that
needs.... well more time and money !! . this, by the way is a great forum for information

[Smiler]

thanks hilton steve
will gladly take your advice and go for twin screws , i dont want to waste time and money and end up with a machine that
needs.... well more time and money !! . this, by the way is a great forum for information

If you go with twin screws, I'd drive them both via belt from a single motor. If you use two motors and slave one to the other and one loses steps you will get racking. If one stalls, you could get a broken machine.

My 2 penneth'

Jeff.

[Gary]

What documentation? would be interested in having a look at that.
When i was technical director at mcp it was policy to strongly advise not to use two motors with one driver.

Although I have documentation from MCP suggesting my drivers are powerful enough to drive 2 motors.....

[HiltonSteve]

To be honest I have never tried driving 2 motors from 1 driver, I was thinking about doing this in my initial design stage because someone suggested it but gave up on the idea.

Well you learn something every day!