Author Topic: Controlling Z axis  (Read 2610 times)

Administrator

  • Administrator
  • Hero Member
  • *****
  • Posts: 2642
  • Administrator
    • View Profile
Re: Controlling Z axis
« Reply #30 on: April 25, 2017, 08:15:23 AM »
It looks to be a very tidy and effective design Ralph and no loss of area.

My only concerns are:
1. The thread pitch looks to be very coarse so isn't backlash an issue? It would have been nice if they had used fine pitch threaded rod giving the tidy 1mm movement per rotation.
2. Also, what is the free play in the sliding plate like; is it enough to cause issues when the the dives accelerate?

Mike

1. The threads are 1/4 28 (28 is fine pitch) and this works as an M6 size as well. I don't understand why backlash would be a concern for you? Can you explain in more detail?

2. I've eliminated almost all of the free play in the laser mounting plate, which is the focusing plate. Not all of it but most of it. As I use it, time will tell if it remains stable in place or if it moves with rapid X axis movements.

Note: while I can't recall exactly what I paid for this, it wasn't over $20.00. This is probably the best design you're going to get for that kind of money (even tho you can't buy it as a stand alone item).

I agree the whole design should work more smoothly and be nice and solid, but that would add to the cost and add to the weight. From a re-design stand point, I have not put pen to paper or keyboard to QCAD -- but -- I'd like to see some kind of bearing movement on two short rails such that the vertical movement is very smooth. And a finer thread count would be better too as you said. This re-design would be a combination of acrylics and metal. I'd probably also include my laser quick connect/disconnect design that I have already done and was previously using.
Admin -- Ralph -- support @ BenCutLaser dot us
https://www.dropbox.com/s/xftw71gccfhyl3y/SetupBenCutLaser2.9a.zip?dl=0
BCL Paid license: $49.95
via Paypal to bclpp@primemail.com

Lob0426

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1622
  • Let the Magic Blue Smoke out!
    • View Profile
    • Richards RasPi Web Server
Re: Controlling Z axis
« Reply #31 on: April 25, 2017, 11:25:48 AM »
Backlash is the movement arising between parts in a mechanism. As you raise and lower the Z axis the looseness between threaded rod and nut and their mounts. The backlash in a coarse thread versus a fine thread is less.

The weight of the assembly will help you reduce backlash. But you will still see some. One strategy for fighting backlash is to always move in one direction. By moving in one direction you have taken out the backlash. This means that if you have to move in the other direction, then you have move farther than needed and come back. So once you start, always move down. You should add some marks, if it does not have some, to your assembly to tell you movement in millimeters or inches to give you a reference.

You can measure the backlash with a dial indicator. By adopting the proper methods you can use that piece reasonably accurately!
Richard
A5 2.5W w/homing switches on L7
A5 2W diode self upgraded from stock 500mw
Printrbot Play. Ext bed, integrated tablet control.
Printrbot Simple Metal
USA

Administrator

  • Administrator
  • Hero Member
  • *****
  • Posts: 2642
  • Administrator
    • View Profile
Re: Controlling Z axis
« Reply #32 on: April 25, 2017, 01:50:51 PM »
I didn't know what his question about backlash had to do with manual focusing. I turn the knob left or right until the focus is there and it remains set. The screw turn is very snug so (I believe) any backlash is removed by your last focus setting.

In other words, backlash with this device is a non-issue if the focusing screw is snug.
Admin -- Ralph -- support @ BenCutLaser dot us
https://www.dropbox.com/s/xftw71gccfhyl3y/SetupBenCutLaser2.9a.zip?dl=0
BCL Paid license: $49.95
via Paypal to bclpp@primemail.com

Lob0426

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1622
  • Let the Magic Blue Smoke out!
    • View Profile
    • Richards RasPi Web Server
Re: Controlling Z axis
« Reply #33 on: April 25, 2017, 05:26:26 PM »
That tells me there is not enough backlash to cause your laser focus problems. I am sure there is some if measured. If it isn't enough to cause a problem, all the better.
Richard
A5 2.5W w/homing switches on L7
A5 2W diode self upgraded from stock 500mw
Printrbot Play. Ext bed, integrated tablet control.
Printrbot Simple Metal
USA