RE: [CAD_CAM_EDM_DRO] Long Acme threaded rod

Steve,
To further reinforce what Andy has said, I have Derlin anti backlash
nuts on my small router. I find that if I do much in the way of
rapids at speeds in 80IPM area, that friction between the nut and
acme gets things quite warm. That is to say warm enough that I don'
want to keep my hand there very long. This is with 1/2" - 10TPI
screws. If you try to get multi start acmes, you can find them, but
the nuts must be made for a particular brand of acme as I understand
the actual thread form will vary from manufacturer to manufacturer!

Art
Country Bubba


At 11:37 AM 6/17/2013, you wrote:

>Hi Steve:
>
>
>
>A couple of observations:
>
>
>
>-even the fiber-reinforced timing belts do not really stretch much.
>
>
>
>-More powerful steppers usually go slower, and for a router, you usually
>want speed.
>
>
>
>Andy Wander
>
> _____
>
>From: CAD_CAM_EDM_DRO@yahoogroups.com
>[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Steve Greenfield
>Sent: Monday, June 17, 2013 11:26 AM
>To: CAD_CAM_EDM_DRO Mailing List
>Subject: [CAD_CAM_EDM_DRO] Long Acme threaded rod
>
>
>
>
>
>Try not to laugh...
>
>I'm working on designing and building a CNC mill/engraver. I'd like it to
>have a cut volume of approximately 1000x1500x100mm (about 3ft by 5ft by 4
>inches) that can cut aluminum plate and hardwood, at most. I expect to take
>multiple passes to cut through an aluminum plate.
>
>I'm basing the design on the ShapeOko machine sized up, using 8020 in the
>25mm size with Openrail hardcoat and grooved steel ball or delrin bearings
>rather than ground rods and linear bearings. The Y travel will have two
>steppers driving it.
>
>Something like this, except the Y rails will be fully supported by another
>piece of 8020 extrusion bolted alongside and the 8020 along the front and
>back will be raised so I can slide a longer sheet in:
>http://powercordlabs.com/1200mm-x-1200mm-shapeoko-build/
>
>Openrail:
>http://openbuildspartstore.com/openrail-hard-coat/
>
>The ShapeOko uses timing belts to move things, but for the size I want, I am
>worried about stretching. So I'm planning on using Acme rod. However, I'm
>worried about a 1500mm long Acme rod whipping. I already have some 6ft
>1/2-10 and there are anti-backlash Delrin nuts available, but that seems
>thin for such a long rod.
>
>I have considered ballscrews, but the price is fairly high and it is cheaper
>to get a more powerful stepper to make up the power loss. Although if there
>will be a significant performance difference, I'll save a bit longer. I am
>not trying for 0.5 thou cut accuracy. I'll be cutting aluminum panels for
>equipment builds (slots for slide pots, holes for controls and buttons,
>holes for displays), and engraving/2-1/2D machining of plywood, hardwoods,
>machineable wax, plastics, etc. Probably the parts requiring the most
>accuracy will be wooden gears for clocks, driven by a stepper motor.
>
>Am I completely off track? There are also steel wire reinforced timing belts
>available.
>
>Steve Greenfield AE7HD
>http://www.linkedin.com/in/stevenjgreenfield