Linear Actuators/Screws

Your local friendly hardware store carries threaded rod in various diameters to 1/2 inch at several lengths to five ft or so, and threaded couplers to suit which might well ride nicely giving a little lapping, when driven by stepping motors, for which drive modules at hobbyist prices are available off the shelf. This might be a rather low cost way of getting started. Not sure that holding one mil at 5 ft range is particularly doable this way though just by turns counting: thats 1:60000 - rather high reslolution, still, you could easily prove me wrong.

BrianW

This was my original idea actually. I remember taking a rather large lag bolt and messing with it. 10 threads per in means 1/10 of a inch per "thread"(per revolution) or (pi/180)*t/(20pi) = t/3600 where t is the angle in degrees. So If I turn it 1 degree it will go .3mils. The larger the diameter the easier it is to turn it 1 degree(or less even). In fact mounting a large gear on it can increase it by a large factor. I remember doing all the calculations a while back.

The idea was simply to attach a large gear to a long threaded rod and drive it with a DC motor(not stepper but could be. Then use external inferometery to determine the precise distance(I was thinking about acoustic methods at the time).

The only problem I ran up against is that there is a lot of play in the nut which will throw off the repeatability. Not sure how it would work in practice. Maybe with a load on the nut it wouldn't have too much play but I was looking for something a bit more professional. The rods I looked at(at lowes), while long(2 feet I think), had rather coarse threads(std 10/in) and hence using something actually designed for what I want would be a huge step in the right directionalthough maybe too costly?

If I can't find any specific stuff suitable for it I guess I should go ahead and try it. I haven't thought about it in a few months though and from what I remember there were a few issues. (although probably minor for any mechanical guy)

Thanks, Jon

There are several home-brew CNC rigs detailed on the net. This CNC router from HobbyCNC gives you the flavor, though it it is not up to your range spec.

BrianW

Thanks, I didn't realize that it was such a popular DIYer. At least then I know it is doable. Problem seems to be doing it cheap yet proper. From what I found it costs a little over a dollar an inch for acme screws(1" steel). Might have to try and salvage some from something ;/

Thanks, Jon

One inch diameter acme rod may be suitable for moving the heavy carriage on a machine lathe. But you are interested in precision drilling, I understood. Think of threaded rod for moving the carriage, and use smooth rods, angles etc for supporting it. More on getting into a CNC drill here.

BrianW

I was thinking about that too because the smaller screws are much cheaper. The thing I don't know is if one would be enough? I was thinking about using 4 screws and one solid rod for the support but this might be overkill and introduces it's own problems? (the smaller screws have more threads per inch which is a plus)

Standard 1.8 degree stepper motors give a linear displacement of about .5 mills for 10 Ths/in(.63 for 8 and .31 for 16).

has 3/8 in 20 Ths/in steel acme screws for about 10$ a foot. The mates seem outrageous though ;/

It would seem that I could use a standard threaded rod and get good precision of if I used a gear to increase the angular resolution. I'm not sure if it is that great of a method though(less torque and slower). I'm going to have to shop around and see what I can find.

There's a site I joined yesterday called cnczone that seems to be a great resource(haven't had time to look at it though).

Yes, I've seen this.. I need something a bit larger though ;/

Thanks, Jon