Dumb Question re graduations
|James Frankland||04/04/2019 15:42:59|
|3 forum posts|
I feel like a real wally asking this but i have scoured the internet to try and find some info, but cannot.
I have a Colchester Triumph 2000. I think it has the english leadscrew.
I cannot suss out the graduations on the crossslide. I seem to set a cut and it doesnt come out anything like im expecting.
I think the dials are in metric.
dials are marked as follows.
Saddle. 0 - 25 and moves 25mm\rev
Cross slide. 1 - 50 and moves 2.5mm\rev
Compound. 0 - 20 and moves 2mm\rev
The problem is the cross slide. I THINK it moves 2.5mm\rev. So, i chuck up a 10mm piece which i want to turn to 8mm diameter.
Advancing the dial to 20 should advance the tool 1mm. Taking 2mm off the diameter.
Is that right? It just doesnt seem to be anywhere near. I must be being dumb somehow.
Unless the dials are english?
I also have the compound swung over for threading but i dont think that should affect the cross slide?
I have some pics but cant get them in here either. double fail...
|James Frankland||04/04/2019 15:48:12|
|3 forum posts|
15038 forum posts
Cross slide take 5.0mm off diameter that is why dial reads 0-5.0 but tool only needs to move 2.5mm to make the cut. A lot of lathes have the cross slide reading diameter.
You say 1 rev of the cross slide moves 2.5mm so 2.0/5.0 should move it 1mm and take 2mm off your bar.
If you are only moving it to the first number than that is 0.2mm, you need 40% of a turn
Edited By JasonB on 04/04/2019 15:58:05
|James Frankland||05/04/2019 10:27:58|
|3 forum posts|
Thanks. That makes sense. I will give it a try later.
|3996 forum posts|
This problem had me going for a bit. I started with a mini-lathe with a dial graduated in depth of cut. When I thought I knew everything about lathes (silly me), I upgraded to a WM280 which is graduated in change in diameter. Took me a surprisingly long time to spot the difference and then get used to it.
|Pete Rimmer||05/04/2019 15:13:32|
|265 forum posts|
Could be that it once had a twin-start cross slide screw but someone made a new one with a single-start thread of the same pitch (as often happens on the Bantam/Chipmaster lathes). It turns the screw from radius to diameter-reading and the dials still make sense (once you've figured out what's happening).
An easy way to tell if that's the case is to use a dial gauge to check the feed rate on the cross slide when surfacing. If you turn the chuck one turn by hand and it only feeds half what the levers are set to, that's an indication of the above.
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