Needs Pictures: 0
Results 16 to 21 of 21
-
20th Jun 2021, 11:09 PM #16I break stuff...
- Join Date
- Aug 2010
- Location
- Toorloo Arm, VIC
- Age
- 39
- Posts
- 1,270
I assume you're using the same pinion each time you tighten the chuck up... Looks like one is marked with a '0'? That should in theory be the most accurate, but check all of them to confirm. Normally one pinion will pull the stock more true than the others.
You could change the countersinks to shallow counterbores, and cut the register on the backplate undersize a bit, make it into a poor mans set-tru... If the chuck is consistently off in the same direction this should let you improve it a fair bit for general use with just the one adjustment.
-
21st Jun 2021, 12:26 AM #17
One thing I noted early in the backplate machining thread and was reiterated in the later bare backplate images is that the spindle nose and thread protrude through the backplate by maybe a full turn of thread.
In another image looking at the thread turned in the backplate with the chuck mounted, the bore in the chuck is chuck is smaller than the faceplate thread, and the back of the chuck is close to the faceplate.
If that is the case, it would be probable that when you mount the chuck/faceplate assy, you are in fact registering the chuck back to the spindle nose because they contact before the register faces of the spindle and the faceplate contact, negating the care in accurately machining the spindle register rebate in the faceplate.
To check this, I would mount the faceplate only and mark the spindle and faceplate alignment and measure the distance from the back of the face plate to the headstock casting, then repeat for the faceplate and chuck combination. If the marks created do not line up perfectly, and the faceplate to casting distance doesn't match, then something is preventing the backplate from registering accurately on the spindle, and in your instance, it could be the spindle nose meeting the back of the chuck.
I may be spouting BS but it is based on what I see in the pics and if so, I apologise in advance.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
-
21st Jun 2021, 10:29 AM #18Most Valued Member
- Join Date
- Jun 2007
- Location
- sydney ( st marys )
- Age
- 64
- Posts
- 4,887
Based on the above comments and looking at bore sizes of TOS 125 mm chucks the bore is smaller than the spindle OD, you may need to use a spacer.
-
21st Jun 2021, 08:35 PM #19Diamond Member
- Join Date
- Aug 2019
- Location
- Revesby - Sydney Australia
- Age
- 56
- Posts
- 1,183
Well spotted. I forgot about that. Some testing today (16mm and 50mm rounds) showed repeatable to about 0.001" T.I.R-o, so I might hold off on stripping the chuck.
You could change the countersinks to shallow counterbores, and cut the register on the backplate undersize a bit, make it into a poor mans set-tru... If the chuck is consistently off in the same direction this should let you improve it a fair bit for general use with just the one adjustment.
But for now, I'm happy with the 1 thou
-
21st Jun 2021, 09:01 PM #20Diamond Member
- Join Date
- Aug 2019
- Location
- Revesby - Sydney Australia
- Age
- 56
- Posts
- 1,183
No apology needed, and well observed.
It would have been a problem, but I bored a spindle cavity in the chuck several days ago, in a bigger lathe:
IMG_1623.jpg
At least 1mm clearance around the spindle (in case I ever re-machine the spigot step on the front of the back plate)
-
21st Jun 2021, 09:08 PM #21Diamond Member
- Join Date
- Aug 2019
- Location
- Revesby - Sydney Australia
- Age
- 56
- Posts
- 1,183
I did think about that. A longer thread through the 5lb weight might engage better on the spindle (though, a smaller register?), but having to remember/find the spacer each time I swapped chucks would frustrate.
Relieving the back of a new chuck was a shame, but seemed easier.
Similar Threads
-
4 jaw chuck
By outoftown in forum THE HERCUS AREAReplies: 1Last Post: 12th Aug 2020, 11:40 PM -
Repairing Jacobs No. 34 chuck.
By nigelpearson in forum METALWORK GENERALReplies: 5Last Post: 17th Jun 2020, 05:13 PM -
Wax Chuck !
By BaronJ in forum METALWORK GENERALReplies: 10Last Post: 16th Sep 2018, 01:17 PM -
collets : to chuck or not to chuck
By steamingbill in forum METALWORK GENERALReplies: 4Last Post: 26th Jul 2014, 10:17 PM -
New 4 jaw chuck.
By Alaks McGREGORE in forum METALWORK GENERALReplies: 25Last Post: 8th Jun 2013, 03:28 PM