How to measure lead screw dimensions for controller setup?

How to measure lead screw dimensions for controller setup?

Postby AlanAndrews » Thu Dec 21, 2017 12:16 pm

Hello everyone,

I recently had the original control electronics on my ELU860 blow. I managed to get hold of circuitry details and had a little success initially with replacing blown components, but it has gone again. So I have taken the decision to remove the old control and motors and retrofit new equipment. I'm retaining all the original mechanicals.

This also means that I'll be able to offer up the motors etc as spares.

The controller needs to be setup with the number of pulses per rotation/mm.

I cannot find any mechanical details of the lead screw, so will need to measure this manually.

Can anyone provide reliable instructions please?

Many thanks
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Re: How to measure lead screw dimensions for controller setu

Postby Timvmax » Thu Dec 21, 2017 7:24 pm

You can work out the pitch of the lead screw by rotating it one full turn and measuring the distance the axis travels.
This won't however tell you pulses per rev, that will depend on your controller, stepper motor and any gearing or pulleys between the motor and the lead screw.
What controller are you planning to use?
There is tons of help on CNCZone and some extremely knowledgable contributors, you will probably even find someone who has already done the same conversion.
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Re: How to measure lead screw dimensions for controller setu

Postby AlanAndrews » Thu Dec 21, 2017 7:38 pm

Yes, I understand that bit but wondered if anyone had a failsafe technique with the measurement. I'm thinking of adding a 360deg TDC dial on the end of the shaft. Clamping a fixed block to the axis travel, winding the axis frame to this, then using a vernier depth gauge to measure the distance travelled. Then doing the calculation re 200 steps x multistep setting.

I'm going for the DDCSv2.1 4 axis controller and pendant. Motors are closed loop variety Nema34. 8Nm for Z and X axis, and 12Nm on the Y axis.

Motor drivers are HBS860H.

I want the option to go

All will be mounted in custom enclosures with suitable controls. I'll retain the original estops and limit switches from the machine.
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Re: How to measure lead screw dimensions for controller setu

Postby PaulRowntree » Fri Dec 22, 2017 4:23 am

I assume that it is a single-start lead screw ...

If you measure the pitch with a good ruler you will get it close enough to choose among one of the standards ... there aren't that many to choose from.

But at the end of the day, it probably comes down to pulses per distance. I strapped a USB camera to the Z stage, put a good ruler on the table, then moved it a few thousand pulses and measured the displacement. The camera allows a measurement to ~0.005" accuracy, so on a 30-40" travel you re certainly good enough.
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Re: How to measure lead screw dimensions for controller setu

Postby wmgeorge » Sat Jan 06, 2018 1:32 pm

Or, just draw say a 100 mm or so square and do a light cut in a scrap piece and measure. Adjust steps until your square is the same as your drawing.
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