Sidney Lathe Cross-Feed Screw Replacement
Hi Again! As I mentioned in my previous postings on the Sidney 14, I would like to replace the cross-feed screw and nut. But before disassembling, I wanted to run by the procedure to get some expert opinions before I start.
I understand that it is relatively simple to get the feed screw out by just removing the two large SHCS that hold in the cross-feed dial assembly, and then removing the back side thrust bearing assembly where it is linked to the taper attachment.
I have one potential problem as shown in the second picture. There appears to be a collar pinned to the feed screw on the near end (top of the photograph adjacent to the lead screw threads) and the pin doesn't go all the way through to the other side of the collar.
So my assumption is that I would have to drill out the pin to get the collar (thrust collar?) off of the lead screw. It appears that I will be able to get everything apart without having to remove this collar unless I am missing something. Then it would be possible to set up the lead screw on the mill to carefully drill out the pin and remove the collar from the lead screw.
Please let me know if this is the correct approach or if I am missing anything critical. Thanks in advance for any help!
Last edited by b2major9th; 02-28-2010 at 01:46 PM.
Reason: embed pictures; add detail
Collar is pinned on to provide a surface for the operator side thrust bearing to sit against. The only possible reason for collar removal would be if you insisted on taking screw out thru front of carriage. It is intended to come out rear after you take off enough of the T/A.
I.E., you unbolt nut from cross slide and slide screw and nut assembly out the back.
It isn't really necessary to remove cross feed dial two bolt housing at all - screw will separate from this assembly at the telescope joint in the act of taking it out the rear.
Your photos are too wide.
Originally Posted by johnoder
Thanks for the tip on removal. It sounds like this job is not going to be too bad.
I do have to remove the collar however to fit it to the new lead screw. Is that correct? Or just make a new one and pin it to the new lead screw and forget about re-using the old thrust collar?
Removal of the lead screw assembly seems pretty easy. However it sounds like I could just make a new thrust collar for the new lead screw assembly and pin it on. Is that correct?
Regarding the photos, I have edited the posting to link to the medium size (I think that will provide sufficient detail) and will scale them accordingly in the future.
My apologies Mike - I did not do a very good job of reading about the fact of replacement and not just removal.
Yes, your choice to remove and use collar again or just make a new one.
Before I assumed screw was bad and needed replacing, I would have those double nuts loose so I could snug up on thrust bearing pair and see if that got rid of perceived "wear" in screw/nut.
measurement of free play
As John suggested, I checked the free play of the thrust bearings....they are pretty tight; no perceptible movement when I lean into the slide with my body weight on the tool post. The lion's share of the free play is between the feed nut and the feed screw, particularly near the center of travel. I used the DRO that the lathe is fitted with to measure the play.
First I backed off the two screws that tighten up the double nuts:
Then, I turned the crank to advance the slide, then set the DRO to indicate zero:
Next, I used my body weight to lean into the tool post to push the slide forward the distance that the free play in the nut/feed-screw assembly would allow:
That I read the amount of motion from my zero position which indicates the lost motion in the feed assembly:
I don't have any experience with wear adjustment, but I would think more than .050 is excessive for an 8 TPI feedscrew, particularly when the ends of travel are not worn so much.
I performed the measurement at the two extreme ends of the travel, and here is what I get
Slide backed off as far as possible towards the user: .035
Slide advanced as far as I dare (it gets very tight and hard to crank): .002
Last edited by b2major9th; 02-28-2010 at 05:16 PM.
Reason: fixed photo links, added content
I need to replace the Cross slide screw as well on my Sidney 14", can you tell me where you got your parts from?
3/4-8 LH ACME thread rod and bronze nuts are available from Roton industries and McMaster-Carr. Be aware that the thread rod from these two suppliers is not machine tool grade in terms of the spec runout, but depending on your requirements is probably much better than what you currently have in your machine.
That is not a huge issue for me since I have a DRO on the cross slide. The nice thing it accomplishes is that it significantly reduces the backlash, and the cross feed is not loose in the middle and tight on the ends.
Three foot length should do the trick. The feed nut will of course have to be adapted to the mounting on the cross slide.
Any chance I can get some pic's of your DRO setup on the sidney?