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+--- Thread: Changing leadscrew pitch (/thread-3762.html)
RE: Changing leadscrew pitch - Pete O - 11-23-2017
(11-22-2017, 07:07 PM)SteveG Wrote: Did you end up making the cross slide screw yourself, or just living with it? I'm guessing its LH ?
Steve
I made the cross-slide screw and nut, the original was 1" 5tpi l/h square thread, I replaced it with acme in the same dimensions and used a mate's lathe to graft the new screw onto the drive gear.
Sorry I can't answer your gearing question, I'm thinking it can almost certainly be done but your thread chart would be obsolete.
RE: Changing leadscrew pitch - f350ca - 11-23-2017
If you were closer Steve I'd cut it for you for that price and use better steel, you know the shiny kind.
If you went with the 6 mm pitch and changed the gearing to the QCGB by a ratio of 6/4 the thread chart should still be correct. By the time you buy or cut the gears though you'd have the same money or time invested.
RE: Changing leadscrew pitch - SteveG - 11-23-2017
Thanks Greg.
I sat down with a strong coffee and a calculator last night as I knew the 6/4 ratio would be the key to changing to 6mm pitch, but I couldn't mentally get my head around how to apply that practically.
In the end I worked out that if I either reduce the input change gear tooth count by 1/3, or increase the output gear teeth by 1/2 then all is good.
For example if the input gear on my current 4mm chart is 90, then it becomes 60.
Or if the output gear is 80 it becomes 120.
The good thing is I've only got the change gears that were fitted to the lathe, so am making the missing ones anyway. Blanks are roughed out to thickness and bored but only 2 are at finished diameter ready for cutting the teeth. If I make the decision to change to 6mm then I'll just cut the gears to suit that instead. I'd definitely be less inclined if I'd just finished cutting a full set to suit 4mm..
I can get 2m of quality 30x6mm for just over AUD$300 delivered (local stock). Not exactly cheap, but not outrageous.
A fair bit of image googling also turned up a image of the gear chart for a 6TPI leadscrew. If I could just find an image of the 6mm chart I'd be set :)
Steve
RE: Changing leadscrew pitch - SteveG - 11-23-2017
The other good news is that I found a source of 22x5 LH leadscrew for my crossslide so have ordered that too. Its from an Chinese ebay seller thermalarc11 so not sure what the quality will be like but for $50 delivered its worth a go.
Steve
RE: Changing leadscrew pitch - Highpower - 11-24-2017
(11-23-2017, 06:46 PM)SteveG Wrote: I can get 2m of quality 30x6mm for just over AUD$300 delivered (local stock). Not exactly cheap, but not outrageous.
Steve
That is pretty close to what a local supplier here gets. About $240US for a 2 meter length. But of course they don't have any 4mm pitch and the 6mm is only available in RH. I'm sure they could cut a custom 30x4mm screw but I would hate to see the cost for that!
https://www.roton.com/products/quick-select-guide/metric-lead-screws/
I went there looking for some acme rod for the tail stock on my offshore lathe. I had them all scratching their heads for the longest time
until they figured out it was a metric diameter with an imperial pitch. I ended up buying a slightly larger imperial rod and nut with the original pitch and had to make it work. Murphy's law in force as usual.
RE: Changing leadscrew pitch - Mayhem - 11-24-2017
Change gear calculator. I cannot find the original source but here is the .zip file I downloaded some time back.
RE: Changing leadscrew pitch - SteveG - 11-24-2017
Thanks - that's very useful.
The note "when both B and C are zero that B can be any gear" suggests it can calculate a simple 3 gear set rather than compound, but I've done half a dozen calcs and yet to see one come up like that, so I'm not sure that part actually works.
Steve
RE: Changing leadscrew pitch - Mayhem - 11-24-2017
My old lathe had a 2tpi leadscrew, so I could get away with a three gear set up quite often.
RE: Changing leadscrew pitch - f350ca - 11-24-2017
The lead screws in my Summit are metric with imperial leads. Metric screws are trapezoidal, so they have 30 degree thread angles instead of 29 acme. The screw for my compound was metric OD, imperial lead and 30 degree profile.
RE: Changing leadscrew pitch - Mayhem - 11-24-2017
Just remembered that I had a photo of the gear chart:
[attachment=15297]
Doesn't help you at all but I thought I'd show it given my last post. Would have hated someone to have given me a Pinocchio emoticon
