|Mark Gould 1||20/02/2019 08:50:20|
|114 forum posts|
I turned a shaft down for a machine that needed one. The long main section (20mm dia) had some irregularities in the finish, almost as if the set up wasn't rigid enough.
I started looking at the cross slide in more detail and stuck a DTI (referenced from the lathe bed) and discovered about 0.06mm in and out movement on the cross slide. By that I mean movement to and from the operator so perpendicular to the bed.
We started paying with the adjusting collar on the cross slide spindle (see pic).
Now for the newbie questions:
1. Is this collar to remove backlash and make the in and out positioning of the cross slide more consistent?
2. Am I right in concluding that this collar, if not correctly fastened will result in the cutting tool being pushed back the same distance as the backlash in the screw?
3. If I tighten this collar and remove almost all of the above mentioned 0.06mm I cannot turn the crossfeed handle at all. Is the trick making a compromise between ease of operation and trying to eliminate backlash?
Sorry for the questions, this new hobby and taken me hook, line and sinker
|Martin Kyte||20/02/2019 09:24:36|
|1463 forum posts|
Adjusting the collar will take the backlash out of the cross-slide bracket/leadscrew interface with the proviso that as it needs to turn freely it will need some clearance. It can do nothing for the backlash between the leadscrew nut and the leadscrew.
|Douglas Johnston||20/02/2019 09:39:53|
590 forum posts
Locking the cross slide during machining will prevent any movement of the slide. The backlash is only a problem during the initial setting of the cross slide.
|Nick Hulme||20/02/2019 09:43:50|
|694 forum posts|
You can use thrust bearings to eliminate any backlash from the adjusting collar system, you do need to machine the cross slide end plate casting to accommodate the bearings though.
841 forum posts
Hi Mark, in answer to your questions Q1 the collar will not alter the backlash between the feed screw and the nut it is there to adjust the the "play" on the end plate and act as a thrust bearing when retracting the cross slide, 0.002" is acceptable and you cannot remove all the play. So No it will not affect the positioning of the tool for the cut applied.
Q2 answer is No! the cross slide is pushed towards the work by the feed nut and the adjusting collar will not be in contact with the end plate during a cut.
It seems from what you say you were getting a poor finish on the shaft you were turning, assuming you were applying a cut correctly i.e. always back off the cross slide then feed in to the point required -- do this each time you are making an adjustment for your next cut when finishing. If you just say feed in another 2 thou on the dial from the existing setting you will not achieve consistent results -- thus back off and come up to the new position.
Also what tooling are you using HSS or replaceable tip tools ? The finish can be affected by many things, material type, the cutting tool, speed, lubricant etc etc. ---- a photo of the work may help
|Mick B1||20/02/2019 09:57:43|
|1124 forum posts|
Backlash is a fact of life on practically every manual machine, and you just have to get used to countering it as second nature. If you try to remove it all - and Myfords give you more capability than some of doing so - you'll find the hand wheel will bind in places and be quite unpleasant to use. You have to arrive at the compromise that suits you best.
Make a habit of ensuring it's taken up in whichever direction makes sure that the slide movement will equal the handwheel movement. Sometimes if the cut's so light that the handle rotates the wrong way under gravity, use the slide lock very lightly just to provide enough friction to prevent that losing your position.
Just my two-penn'orth.
3651 forum posts
How long was it? Could be if too long there was flex in the centre section. If so, a travelling steady may help. Cross slide backlash is unlikely to be the culprit. Plenty of work done well within .001" on lathes with .020" backlash on cross slide screw.
|1212 forum posts|
Mark Gould 1:
Is that illustration from Bradley's Myford manual?
Another excellent book is George Thomas' ME Workshop Manual which I think would answer most of your queries.
There is always something to learn: I bought a replacement "diaphragm washer" from Nottingham Myford and was stymied by its failure to work as expected; they patiently explained that you need to bend it by tapping with a soft hammer!
|Mark Gould 1||20/02/2019 13:36:25|
|114 forum posts|
Amazed at the responses, all welcome and informing. Many thanks for that and it will take a while before everything is clear to me. I am unschooled in metal works and am learning on the fly. This forum and ahum, youtube.
I understand that it won't change the backlash, thanks Martin and JohnF. My understanding on how it works was flawed but it is slowly becoming clearer now.
I use inserts tooling (all 10mm due to tool centre height). Some Chinese cheapy inserts, others are known brand (Sandvik, Mitsubishi) DCMT and CCMT inserts.
The bar was 300mm to start with, the finished shaft is about 230mm.
I was turning at 640rpm.
@ega, I found the illustration when Googling "Myford Super 7 cross slide friction" and came across it on another board. I am not sure who's illustration it is, sorry. I will look into that book and dito washer!
Thanks again gents,
|Clive Hartland||20/02/2019 13:46:11|
2455 forum posts
There is a bearing modification for Myford cross slides, see ARC's page for details which needs a bearing and modification of the spindle mount.
To do mine I used the mount off my vertical slide so it was a straight swop.
Find details in Arc's page under projects at the bottom of the listings.
4650 forum posts
It can be difficult to get the gib adjustment right so as mentioned it can help to lock the slides bearing in mind that might alter the cut. An auto feed helps as it is difficult to hand wind it smoothly and hesitations do show up even though no change in cut depth is measurable. Lubricaton can help, especially for HSS and trapped chips can cause scoring. Is the marking periodic or random?
edit. you can use emery and wire wool - we won't tell
Edited By Bazyle on 20/02/2019 14:04:58
271 forum posts
Clive, interesting point you made about using the mount off your vertical slide. I have just modded my cross slide with the thrust bearing assembly (see my other post) and while my cross slide was out of action I thought I would fit the one from my vertical slide, but it was different and wasn't a direct transfer?
I managed to use it by clamping it on the end of the cross slide with milling clamps!
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