A different (better) kind of screw

[Pat2000]

Originally Posted by posix <snip> Gears help but can someone on here with home-shop tools make a 3.75mm diameter roller with 10 tooth on it and a 23mm ID nut with <insert the calculated number of teeth here> teeth to engage all rollers equally? Doubt it. I know I can't. So you make do with that you have.

Posix, I don't know if the rollers have to be so small, but then again if you want six or so... maybe we are back to looking at less? keeping them reasonably long still gives a lot of contact and hence load carrying capability?

ok if we make them big enough it shouldn't be too difficult IMHO (ok I have some access to a small worksop at work) to perhaps broach those teeth on?

I'm reckoning that no great precision is needed just the requirement that the rollers must not be allowed to slip very far - maybe I'm kinda guessing wrong there?

well particularly if you can use Delrin it broaches real sweetly !! the internal gear teeth - I don't think that the number of teeth would be important? on some of the piccys that internally toothed ring looks like a seperate part - might be best me thinks!

Now I was dreaming the other day of how to use a single point broach to broach multiple teeth around a diameter without using a rotary table. on a 3 axis CNC mill. I must have a go sometime... take too much to try and describe will maybe try to explain on another thread.. if time permits

[posix]

I have my set of 3 roller screws. But I think that the decision to go for a cheap off-the-shelf M10 "allthread" was a wrong one. I should've asked for a steel M10 allthread to be made on a lathe for me. As it is the roller screw is a bit dissapointing as the cheap allthread isn't exactly to tolerances so it wobbles a bit as the space between rollers and lead screw isn't the same throughout its travel but fluctuates somewhat. Serves me right for not having take this into consideration before I had these made. But it would now be a simple matter of having a precision M10 rod made and then use that for the rollers. The rest can be reused. I think.

[svenakela]

Hmm... I have a set of three ballscrews without nuts, maybe should convert 'em to rollers?..

[posix]

You can't as the ball screw shaft is a "female" pattern -v-v-v. You would have to make a "male" roller -^-^-^ and that would be too much effort to be honest. You need something "unisex" - i.e. it has to be the same on both sides. And the only thing that fits the bill is a seesaw thread like so /\/\/\/\

Much easier to just find a piece of hard rod and start from that.

[Pat2000]

Originally Posted by posix I have my set of 3 roller screws. But I think that the decision to go for a cheap off-the-shelf M10 "allthread" was a wrong one. I should've asked for a steel M10 allthread to be made on a lathe for me. As it is the roller screw is a bit dissapointing as the cheap allthread isn't exactly to tolerances so it wobbles a bit as the space between rollers and lead screw isn't the same throughout its travel but fluctuates somewhat. Serves me right for not having take this into consideration before I had these made. But it would now be a simple matter of having a precision M10 rod made and then use that for the rollers. The rest can be reused. I think.

Thats a bit sad... the threaded shaft must be consistant throughout it's length.. you've got me wondering how they make that 'studding' I believe though I'm not sure... anyone?... that it would usually be rolled and I'm thinking does that produce a thred that is consistant throughout it's length? if you only want a shortish length then matbe you can get one turned but be careful if it's screwcut without any support on the sharft then that would cause it's own problems.

I was wondering about using Stainless steel - do they still roll that stuff?

[posix]

Well now you mention the supports when I spoke to this chap about making me a threaded rod with my spec thread depth, angle etc he immediately asked how long and that it should be done with supports - I don't know their proper name but lathe people will know what I'm talking about.

And you know what the saddest part is? All that time I had a 1m piece of 20mm hardened steel rod in my car!

[Corvus corax]

Svenakela, I have the same problem. I just bought three lengths of 1 inch precision ground ballscrew, but the nuts are all missing! I did figure out a way this could be done with them, though. If you have plenty of screw (as I do), you could cut three small lengths of the parent screw to make each nut. You then have only to fill the tracks with something round (surface ground mild steel or brass) in the proper cross section on the satellite rollers, and you would have an efficient set of mating rollers. Due to the large surface area, I would probably be able to get away with using 1.5 inch satellites on my 1 inch diameter screw.

[JBV]

Made a model of a recirculating nut (i think this is the one most suited for diy)! Seem very doable! Have to try it The problem with this design is that you can't use it as a rotating nut. But i guess you just have to make the spacers of metal and connect them to the housing in some way.

I belive you could get very good results if you use a threadmill and a rotary table on a mill! Easier than doing it on a lathe, and you could make smaller rollers and ID of the housing!

/Jay

[greybeard]

Corvus
Any chance of finding springs of the right cross section that would grip your "rollers" as thread fillers ?

[svenakela]

Corvus: Isn't irritating, the lack of nuts?
I was thinking of making a couple of rollers that are not threaded, just with grooves, to run with the ballscrews (nope, not hard to do if someone you know have a CNC-lathe). Something like the german design I've mentioned earlier in this thread. My main question still needs an answer: What happens if the rollers stops? Even though the rollers are not threaded the gearing will change and I don't want a "dynamic gear ratio"...
I was talking to a workshop that makes threaded rods, and HOLY CRAP there was a big difference in price when I questioned for better precision. That's why Im going to test my ballscrews, I already have them and they are useless...

JBV: Very nice assembly! Sure you can use it as a rotating nut, why shouldn't it work? As Posix has mentioned, the rollers are supposed to roll, and then it doesn't matter if the nut is rotating or the screw. The relative movement between the parts is the thing that counts.

Cheers,
S

[JBV]

Yeah but in my assembly the spacers are made of nylon or some other plastic and not connected to the housing, and if you turn the housing they almost definitively would slide You have to transfer the rotation of the nut to the planetary rotation of the rollers without "losses" if it's going to work predictable and with any degree of accuracy.

Should be easy to integrate the spacer in the housing (and endcap). I'll try to make a more advanced model! Think it would be a good idea to have wipers on the nut?

/Jay

[JBV]

What about using the same kind of leadscrew as rollers and just turn them down and the ends with a groove?

The housing is a bit harder to make but i belive you could make it in separate pieces and bolt together. Perhaps with some kind of preloading of the ridges the rollers rides on

Suggestions for the spacer? I have some ideas but they are hard to assemble!

/Jay