Thread: Large Build Small motors...Will this work?

Welcome to the forum.

You haven't said how you are driving the Y axis. Are you using a screw, rack and pinion or belt and what gearing?
Generally if you have a 5mm pitch screw you will be able to drive a Y axis at around 1200mm/min. This is based on my experience with these steppers and the Xylotex board. Lots of factors come in to it so do not take this as read.
Motors and boards are easy to swap out later so at this stage keep building and see what you end up with.
Steppers have more torque at lower speeds so try to keep your gearing high to use this torque. The trade off is resolution but this will be minor and if your backlash is minimal then you will have repeatability which is much more important.

Thanks Rod. I am still in the building process and have not determined what I will use to drive the system. Whatever will work best I guess. Acme rod would be the way I prefer. I think this will whip too much at 8 feet. What would you do? I will be making about 30 feet of cut per a 4x8 sheet of osb and I have lots to do. I want to have enough power to push a small router bit to cut the osb into pieces. The rest of the time I will use it for plasma cutting which should be easy going.

Yes 8 feet will be too much for a screw. The popular method is rack and pinion but you need to be able to machine the pivot for the pinion - meaning you need to have machines that can do it.
Have a look at the Mechmate site for ideas and there are plenty of buids on their forum.
http://www.mechmate.com/
There are a couple of R&P builds on this site that would also be worth looking at.

What would you think about using a chain drive. It is much cheaper and readily available where I live.

I don't know why but I am going to say no. My thoughts are there is probably too much backlash in a chain drive and chain can stretch so you will loose calibration of the machine.

Nothing wrong with chain drive but you need to build tensioners into the setup.
Chain drive is also a good substitute for rack and pinion and gives similar resolution/accuracy to r & p.

There used to be a highly regarded commercially made chain driven Industrial cnc machine in the US. They only converted to r&p due to uniformed perceptions that r&p was superior.

If you spent some time searching here you should find discussions about chain drives but the discussions were some years ago and may be hard to find now.

Bob,
I did some research after my last post and found that there are different grades of chain for different things. For the purpose here chain falls into two categories - transfer of power between points (eg bicycle chain) and for maintaing a reference between points (eg valve timing chain on car). CNC would fall into the second category and require different grade of chain to so say a bicycle chain. I can remember my bike chain stretching and having to adjust the tension every so often.
One would have research this carefully so that dollars and effort will not be wasted.

Bob,
I just found an actuator on ebay that had a chain sprocket drive. Goes to show chain drives are still being used out there.

I am thinking of trying a belt system. This seems to be very cheap.
Now if only I could find some cheap v bearings.

http://cgi.ebay.ca/Polyurethane-Timi...742.m153.l1262

You might find the bearings you're looking for here.

This is the most economic place I found when looking.

http://www.superiorbearing.com/docs/...ls_wheels.html

Greg