A different (better) kind of screw

[Mike Everman]

Hi Ian, I take all your points as valid! One of the patents I cited early in this thread talked extensively about the proper curvature of the groove flanks to make it right, which I was hoping it would bed into on both screw and rollers, then back it off to smooth running. so the theory goes...

[handlewanker]

Hi Mike, hope it works out OK for you, can't wait to see progress.

About a year ago I bought another Milling machine, an Ajax, like a Bridgeport, but bigger, because it was not only cheaper (on Ebay where else), but had auto feeds and fast traverse on all axis.

Long story short, during the transfer of my previous mill, (a Bridgeport), to my mate's factory, and the installation of the Ajax mill in my garage workshop, I assisted the transport people with a pallet truck I had, that had a 2 ton capacity, and as the mill was 1-1/2 tons it worked out OK, bringing the mill in from the road up the concrete drive way and into the garage.

Now the wheels on the truck are made from a hard Plastic type material, can't say what type of plastic, probably Nylon, and in the process rolled on the concrete floor without any deformation.

So......supposing the grooved rollers of the roller screw are made from a hard nylon type material, I mean really hard stuff, they would probably mate with the screw thread without each other trying to reform themselves, but as they would be slightly resilient there would be a certain degree of resistance to "reforming" the thread and/or grooved roller profiles.

The problem with roller technology is that it requires hardened surfaces to roll together otherwise one tries to deform the other, but judging by the amount of pressure the pallet truck rollers supported there was no reforming of the wheels at all, and the front steering wheels (2 of them) are about 150mm diam X 70mm wide, but are coned so that only the middle 30mm of the wheel contacts the concrete and takes the weight.

I think if the roller has at least 6 grooves in contact with the thread flanks it would withstand the axial loading of the drive thrust, as this would not be in the order of tons but lb's, and the radial line contact of the groove and helix of the thread would mate fairly well due to the resilience of the plastic, provided the top corners of the screw thread were slightly rounded off to prevent cutting into the plastic.

I cite this phenomena as an observation that if the pallet truck wheels were made of cast iron, steel or bronze thay would, by point contact, chew the concrete up in five minutes and on a prolonged useage on concrete would themselves be reduced to bumpy flats.

I've just finished rebuilding the gearbox of the Ajax, as it had a bronze worm wheel shredded in it, hence the cheap price on Ebay, so haven't had time to put any theories to practice.
Ian.