A second approach to a CNC machine!

[chuckknigh]

Well, I went to one of those tool sales they hold out in the country -- some little company (Homier is a common one) sets up in the local VFW hall, and sells tools to us country folk. Today, it was Cummins Tools.

Well, while I was there, today, I found a drill press vise. It is essentially an X-Y table. In fact, it reminds me of a crude version of the X-Y facility on the Harbor freight mini mills.

http://www.cumminstools.com/browse.cfm/4,92.htm

It has acme lead screws which move the table in 2 directions, and a built-in clamp on the top. Surprisingly nice, actually.

It's a fairly rough casting, but it has dovetail ways and a built in facility for shimming them to remove slop! The actual sliding surfaces aren't too bad, either. Once I take it apart, clean it *properly,* and hopefully finish a few of the surfaces it ought to even look good!

I've not measured its exact capacity yet, but just eyeballing it, it looks like it's about 4x6 inches of movement, or thereabouts. The vise capacity is 4".

Anyway, needless to say, for $19.99 I picked it up. I think it'll make a nice complement to my wooden router, if I convert it to CNC. Might even allow me to do some light metalworking!

A question, though. The ACME nuts are part of the castings, so I can't remove, replace, or upgrade them -- is there any way to add backlash compensation, or just generally "tighten it up," perhaps with an injectable polymer compound? Something to take out, or at least minimize the backlash?

I'd just *add* nylon nuts to it, but they'd take up a bit of room, and basically eliminate half of its travel!

There must be a way to upgade the hardware itself -- relying on software to compensate is not an ideal solution.

-- Chuck Knight

[wms]

Chuck,

Run a search on this forum for "Moglice"

There are several thread that deal with just such a thing.

[Ken_Shea]

Chuck you mentioned to tighten up the acme backlash by the use of a polymer injection. In the auto repair field for many years I have used this method with great sucess on king pins, tie rod ends etc. This of course was with a special polymer but you may find that even the use of glue gun polymer that it may do what you need.

Just drill a whole in the center of the threaded area and inject the glue gun polymer and see what it does, cost nothing, is reversable and may just be a simple solution.

let me know if you do it and how it turns out.

Ken

[wms]

Ken,

That sounds like a good idea. Call the patent office.


And oh ya how about saw dust in the gear box?

[Ken_Shea]

Ward,
I know it sound like a hoot, but I have injected a bunch of this over the years with really great success, especially helpful in antique cars where the original parts are not available. Glue gun is actually not a glue but simply cheap polymer.

Does saw dust works well in old gear boxes.
Man that really ages us doesn't it Ward?
No one under the age of 40 would know anything about that.

I still have some polymer left you need an injection? great for worn out joints, knees, elbows etc.
Oh, I forgot I do have to drill a hole!!

[wms]

Ken,

I really do think that sounds like a good idea....


I just threw the sawdust part in for a laugh.

[chuckknigh]

Hey, hot glue is nothing more than a medium temperature thermoplastic. Nice stuff for a lot of uses.

A couple of concerns, though. Would it resist wear sufficiently to function as a lining for a screw drive?

It's somewhat springy, so would it introduce backlash into the system? (Tiny layer shouldn't be too bad, but it's still something to consider)

Would it introduce a lot of friction into the system? And, on a related note, would use at a "normal" speed generate sufficient heat to melt the polymer, thus ruining any alignment I had beforehand?

Is there a release agent for it? I'd hate to inject it, and have it stick to the lead screw.

A consideration about its installation, too. I'd have to practically bake the vise in the oven to heat it up sufficiently...the part would have to be hot, as well as the glue, since the glue would freeze "solid" the second it hit cold steel. Might be a bit of a practical problem in this...

Still, overall a good idea. Is there not a nice polymer that cures chemically, that would do the same thing? If I have to, I'll just go get some JBWeld and tap a new hole...but there's no guarantee the tap will align perfectly with the lead screw. They're rolled, not ground...thankfully they're short!

-- Chuck Knight

P.S. Moglice is essentially a granite hard epoxy, isn't it? Somewhat like the JBWeld I mentioned before. If memory serves, it's used to rebuild bearings...a good suggestion.

Is it possible to get a TINY bit of this stuff? I don't want to rebuild 2 nuts, and have buy a pound of the stuff. Since it's for machine tools, I have the sneaking suspicion that it's rather expensive.

P.P.S. On a 60 degree thread, there is a thin "sliver" of a nut called a jam nut, that I can buy at my local hardware store. Looks like "half" a nut. Is something comparable available in ACME? If so, I might be able to use it to adjust out any backlash, using some of the split nut designs -- this option would take up the least space possible, I would think...short of modifying the existing hole.

-- Chuck Knight

[NeoMoses]

you might take some all-thread and a cheap nut/bushing and try casting your own "moglice-like" nut out of JB-weld. Once cured, they both have very similar properties, so it just might work and be much cheaper.

[Ken_Shea]

Chuck never really gave the hot glue any serious thought, it just popped into my head and I threw it out as food for thought. There have been many times something said that was nut usable but prompted ideas that were.

I would not think you could turn these fast enough to cause any friction heat.

I have some hot glue that actually kinda hard and most hot glue melts at very low temperatures maybe 200f?.

I like the idea of the JB weld mentioned by NeoMoses, you could call the company and ask them what a good coating would be so it would form to but not stick to the acme thread. Get a syringe minus the needle from a vet or doctor and use that to inject it . My guess is it would not take much. I have seen epoxy glues already in a syringe and it mixes as it comes out.

good luck, and let us know what you end up with.

[HomeCNC]

I used HOT glue on both exposed ends of my home made pre-loaded ball nuts as a wiper to keep chips out. It works great! Forms to the screw but does not stick because of the thin layer of oil on the ball screw.

[cbcnc]

Hi,

Polyvinyl Acetate or PVA is used when laminating with epoxy in molds. It might stick to a clean leadscrew and not allow the JB Weld to bond to it.

Chris

[chuckknigh]

Well, I have an email in to the JBWeld people, to see if anyone has tried this before. Surely I can't be the first...

Turns out they're located in Sulphur Springs, TX...less than 100 miles from me. Who knew?

Anyway, I did a little digging on Moglice, and other than a friction reducing component, they seem to be essentially the same stuff. Same properties, and everything.

Hopefully it won't be too difficult to make this thing, successfully -- I really don't want to modify the original casting, if I can avoid it.

That way lies madness.

-- Chuck Knight