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Adding 3rd stud to drummond

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Nobby16/02/2011 21:50:28
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587 forum posts
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Hi
I wanted a slower feed on my drummond lathe so I added a 3rd stud and arm. I tryed work out the feed per rev. ? but with no luck .By hand its about 3&1/2 thou per rev.



ady16/02/2011 23:50:15
612 forum posts
50 photos
Give us the geartrain numbers and we'll figure it out for ya nobby.
 
eg
spindle20
1st 50/20= 20/2.5= 8teeth c/f
2nd  60/30= 8/2= 4 teeth c/f
3rd  60t leadscrew for final calc 60/4= 15x8tpi= 120tpi
 
1000/120= about 8.5 thou
 
a 100 tooth on the leadscrew would crank things right down
been at ra pub again tonite so e&oe...*hic*
 
 

Edited By ady on 17/02/2011 00:13:20

ady17/02/2011 00:42:31
612 forum posts
50 photos
Is that an extra wee one on the top? a 30/20?
 

gives 180tpi= about 5.5 thou
 
small problemo though, the leadscrew will go backy wards.
Nobby17/02/2011 11:23:07
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587 forum posts
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Hi ady
Thanks mate . I have had a better look this morning On the spindle/ mandrel is a 20
1st stud 30-20 2nd stud 50-20 3rd stud added 55-20 Leadscrew 60.
The 8 t.p.i leadscrew rotates forward . Its a bit warmer in the workshop today.
Nobby
 
 
mgj17/02/2011 11:24:20
1017 forum posts
14 photos
Do the Drummonds not have a tumbler reverse lever for the leadscrew? If so, that would get round the problem quite easily - what was forwards becomes reverse and vice versa.
 
But you are right, the new set up will reverse rotation, so one will have to introduce an idler of any size somewhere in the train.
ady17/02/2011 12:33:22
612 forum posts
50 photos

20x0.66= 13.3c/f
13.33/2.5= 5.33c/f
5.33/2.75= 1.94
 
60/1.94 = 30.93x8tpi= 247.5tpi
 
so a midgies thumb over 4 thou from the looks of it

Edited By ady on 17/02/2011 12:34:04

Nobby17/02/2011 13:14:21
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587 forum posts
113 photos
Hi mgj & ady
It has not got a tumbler gear like my super 7 mk 1 The slot were the belt tension arm is you can fit an idle gear. I willl have another go with the calculater and work out the t.p.i from that I can get the feed per Rev
Cheers Nobby
Eddie17/02/2011 14:22:01
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56 forum posts
Hi Nobby
Avoid the calculator, and the teethcounting...
Set up a clock gauge and turn the chuck 10 revolutions.
Take the reading on the clock gauge/ 10 that will give you the Thou/rev
Eddie
mgj17/02/2011 17:58:41
1017 forum posts
14 photos
Well 4 thou per rev is a pretty useful general purpose feed for a decent finish, so it looks as that bit of it is sorted.
 
Just the idler gear then. Anywhere in the train Nobby, any size: it doesn't affect the ratio at all
AndyB17/02/2011 20:44:47
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167 forum posts
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Hi Nobby,
 
The jaws on the headstock (the second photo shows the bottom jaw at the top) are for mounting idlers and tumbler reverse.
 
The Drummond site has plans for one (you will have to register but it is well worth it; tons of info from like-minded people) There are also various plans for fine feed arrangements.
 
 
The tumbler reverse is worth its weight in gold so well worth making one if you can't get an original.
 
Andy
Nobby18/02/2011 18:10:53
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587 forum posts
113 photos
Hi Guys
Thank you all for input on this . I tried eddies idea 4 thou easy . I will get on website as A.B . mentioned . Back to scewcutting this lathe is great as it does not double up when you engage lever similar to the X lathe. Yesterday I cut 20 tpi with no problems. as you may have seen I fitted a 125 Micrometer dail on the leadscrew.

mgj18/02/2011 20:17:06
1017 forum posts
14 photos
It looks in lovely condition Nobby - a credit to you.
Nobby21/02/2011 23:07:27
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587 forum posts
113 photos
Hi Ady
Cheers Mate
To avoid drilling the casting for the brass zero line to keep as original I made a steel clip that just clips over. I made and fitted a micrometer dail to my Drummond hand shaper.
I have just bought a small Drummond Little Gooiath but just the basic bed head and tailstock. Its noy here yet . More problems ?
Nobby

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