thanks to MEW
|461 forum posts|
|Time to stir up the waters a bit... |
One has to learn something new every day they say, so I dived into that beginner's article in MEW 184 again. And for sure: there is something to learn, esp. on page 17!
First thing which surprised me no end is the thesis that "advancing the cross slide 0.01 in. on most hobby lathes reduces a bar 0,02 in in diameter". Well I changed the wording a bit, but I hope you get the gist.
Wouldn't it be nice to know which hobby lathes don't produce such a reduction, as seemingly there must be some exceptions? And the professional lathes - how do they work? Many difficult questions for a beginner... I have to ceck how my lathes behave in that task.
A few lines later I learned how to correctly use a clamping type knurling tool. Now I built mine more than a quarter century ago, but to my shame I did it wrongly all the time. Correctly, the clamping screw is only used to spread the rolls a couple of mm (or sixteenths if you prefer). Then you use it in the time honored method of pressing inward - with the cross slide - onto the workpiece. Don't worry if it is only a 3/16" silver steel, for sure the resulting pretzel scriber will be ergonomically adapted to your hand!!!
Continuing the learning process,
Hansrudolf the diligent follower
|Richard Parsons||26/11/2011 18:12:14|
645 forum posts
Ah Hans Rudolph. It all depends on how your cross slide dial is calibrated. On the Myford it indicates the amount you are advancing the tool. On my big Warco the dials indicate how much metal is being removed. It is a bit of a nuisance.
There is also another difference between lathes. The biggest difference is noticeable on the lathe apron where the controls are in different pattern. There is the ‘American Pattern’ which is the reverse of the ‘U.K. pattern’.
I actually have a problem with the Warco. I set on the cut I require and often have to make several passes to get the set cut. I can find NO ‘shake any where. Any one any ideas?
|Stub Mandrel||26/11/2011 21:01:23|
4311 forum posts
Richard is right, some lathes are calibrated to show the change in diameter, not the infeed. Some DROs can be switched into a diameter mode.
I wondered about the knurling bit. It seems to be saying that you should still push a caliper tool onto the work from the side. I always position it on the work and gradually tighten it up - and get good results (viz. the knurled wheels on the surface gauge).
Going in from the side seems to miss out on some of the advantages of the caliper tool.
|461 forum posts|
Here I am again...
Dick, you are too fast.... Please read the sentence again. It clearly says 'advance 0.01 in', not 'advance ten marks on the dial' or something like that. 0.01 in is the same always (imho), whatever numbers your dial marks may show.
As I don't know how you use your knurling tool, I can not answer. But the tool is very clever, I am tempted to make something similar. Hats off!
Neil: same as I said to Dick. Seems you are the first who realized the knurling tool problem.
The wheels have to touch at 12 and 6 o'clock, not 8 and 10 (or 2 and 4 if seen from the other side).
Back into the woods:
1935 forum posts
Well said Versaboss,
For a beginner this is all very confusing, I thought such articles were meant to clarify things?
1935 forum posts
The photograph on p. 16 of the beginners article referenced by Hansrudolf certainly doesn't appear to be 32 mm diameter.
|Steve Garnett||26/11/2011 23:06:19|
|837 forum posts|
Whilst I can see exactly what Hansrudolf means, I must admit that my initial reading of the sentence made me think something rather different - that there's enough 'give' in some machines for the advance of the cross slide by the amount stated for it simply not to travel by that amount at all.
In defense of Mick, though, I have to say (after several hundred thousand words of doing it myself) that conveying meaning in an accurate and conversational manner is quite a tall order, and I'm not at all surprised that the odd ambiguity or inexactitude slips in.
In this particular instance, I wouldn't necessarily have changed the offending sentence, but I certainly think that I would have clarified it.
But as others have said, this is the section about knurling, and I'm not at all sure why it's there in this form anyway. In the middle column of page 16, Mick clearly states that he's in favour of the 'top and bottom, self-centring style of knurling tool', but when we get to the actual process, we are told to set the wheels so that they are 1mm less apart than the stock diameter, and then advance them forward by the aforementioned 0.010in. - which sounds like a right old mix-up of both procedure and units!
All things considered, I'm with Neil on this one - that's the way I've always done it too.
Edited By Steve Garnett on 26/11/2011 23:06:50
1473 forum posts
I think I'm using my clamp type knurling tool in a slightly different way to others here.
With the job turning, I advance the tool until the knurls are at about 6 and 12 O'clock to the workpiece - let's call it top-dead-centre (TDC). I then nip the adjuster down by hand, until a pattern just starts to form, at which point the tool is retracted a short distance. The adjuster is turned a couple of graduations to bring the knurls closer together and is again moved to the TDC position.
I do this until I'm happy with the pattern being produced and then traverse the tool along the part as far as required.
Doing it this way means I don't need to use any force to turn the adjuster (spanner) and there is virtually no side thrust on the mandrel bearings, because the tool tends to be dragged into the job by the lower knurl, whereas the upper knurl resists to some degree, which kind of helps to even things out.
Edited By blowlamp on 26/11/2011 23:40:00
|chris stephens||26/11/2011 23:44:16|
|1048 forum posts|
There is a convention that on Metric lathes the cross slide dial is calibrated for diameter reduction, whilst Imp lathes it is marked in movement, ie radius reduction. There are exceptions, as some of you will not doubt site, but I am quoting the late Mr Moore of Myford fame, and I believe most of you will agree that he knew a thing or two about lathes.
As for the movement, how about this as a thought, the oil on the cross slide screw acts like a "spring" that compresses on heavy cuts but not on light cuts, resulting in very light cuts not being always being in agreement with the dials, but heavy cuts will.
|997 forum posts|
I have seen this time and time again with either incorrectly adjusted gib strips, tool height, lack of rigidity very likely.
Had same problem with my old ML7, had to send carriage down several times same with a chinese geared head screw cutting, wind in 2 thou = nothing, try again, try again, then wham 15/20 thou off. Theres movement some where.
Halving DRO wont work, it halves all axis.
So you might get Y axis to register correct at the expense of X axis being halved, its a right pain. Easy to measure diameter just worked, zero DRO then calculate how far need to go, glad they come with calculators.
I am tempted to get half linear increment magnetic strip if available, problem solved.
Old scrap Harrison 140 1965 was a pure metrc lathe, hand wheel calibration resulted in amount taken off diameter, same as the Harrison 11" imperial and dual imperial/metric M300.
|Chris Trice||27/11/2011 00:22:53|
1362 forum posts
I've always knurled the way Blowlamp does too.
|Jeff Dayman||27/11/2011 00:36:13|
|1976 forum posts|
Having not seen Richard's actual Warco lathe, I can't guess exactly why he needs to repeat cuts at same setting. However if it has the usual towering cross slide and compound rest as used on many far east lathes, flex and play in this system can result in dimension set not being dimension cut. The cross slides on many far east products have a very small footprint on the bed, poor gib support underneath the bed, and a very tall compound slide. This whole rig can and does flex quite a few thou in a heavy cut. I've also seen some where the cross slide nut was a bad fit in the slide, which would allow movement even when backlash had been taken up. On others the flat horizontal contact surfaces in the cross slide assy were crowned and not flat or concave, so even when clamped, slight rocking can happen.
On one far east lathe of a friend of mine, we were trying to track down similar set vs cut problems and I installed a few DTI's to check rigidity and asked friend to make a medium cut. Under load, the toolholder was moving toward him .008" and headstock was moving away from him .004" at spindle height! There is no way that this lathe would ever turn to size without extra cuts to take out the springback. This lathe was a disaster on many levels and at one year and two months after purchase, just outside warranty, the motor caught fire and failed completely. A week after the motor was replaced the spindle bearings seized solid. No replacements were available. That was the end of that lathe. I felt great when we tossed it off my truck in the scrap yard. He later bought an ex-industry well worn Colchester bantam for less than half what he paid for the far east disaster. That was 12 years ago, he's still turning exactly to size every single time, and loves the machine.
Edited By Jeff Dayman on 27/11/2011 00:36:37
|alan frost||27/11/2011 04:42:24|
|137 forum posts|
I think your high regard for the English sense of humour is a little misplaced these days judging my some of these replies. By the way I hope thats a Dutch Hans-I would hate to think a German reindeer was teaching the English about humour These days I think the old Italian proverb "People who live in Turin should not wash their face in the local river " applies too often. The trouble is it seems to be English tourists who are doing this,not the locals..
I took your point (and English apologies for those who did n't ) about the cross slide movement although I have owned lathes that did not reduce the diameter by 2x when the crossslide was advanced x. Its called non-deliberate decorative turning and avoids the need for an elliptical chuck but not the need for a new lathe.
I'm not going to knock the author of the beginners series though. It really is leading with your chin as we've all got our own ways of doing things. At least the man's writing, and on the whole its pretty good, and probably a brave thing to do.
Best regards Alan
A PS. Hey, I just read "back into the woods". Please confirm my suspicions of paragraph one are incorrect.
Edited By alan frost on 27/11/2011 04:49:23
Edited By alan frost on 27/11/2011 04:51:21
1935 forum posts
To quote Hansrudolf's first posting, he says:
"One has to learn something new every day they say, so I dived into that beginner's article in MEW 184 again. And for sure: there is something to learn, esp. on page 17!"
P16 is in that article.
|John Shepherd||27/11/2011 09:04:33|
|218 forum posts|
OK - I read the section on knurling and for the type of tool illustrated it did not make sense to me as well so perhaps there needs to be some follow up explanation in the article?
On the other hand lets not 'throw the baby out with the bath water' - there is some good information and experience imparted in the series and it is by and large an easy and enjoyable read.
I hope this anomaly and the criticism will not discourage those new and old to the hobby from reading the series. It would be a pity if the integrity of the whole series was put in question for what appears to be a minor slip up.
I think the author should be congratulated for putting his head above the parapet, he must have known there would be some feedback and he does not come across as an arrogant type like some that infer they have been 'doing it this way for 30 years so it must be right'.
If there is need for comment perhaps it should be more concise and constructive to help the beginner rather than confuse the issue? I am all for discussion and debate and often get more information and enjoyment from posts that go off at a tangent but perhaps this is a case were intervention by a moderator to split the thread or similar would be acceptable?
|Stub Mandrel||27/11/2011 11:10:33|
4311 forum posts
> Halving DRO wont work, it halves all axis.
> So you might get Y axis to register correct at the expense of X axis being halved, its a
> right pain.
It depends on the DRO you are using. Some of the cheap ones have diameter mode built in to the individual scale. My readout box has diameter mode as an individually selectable option for each axis - but I made it that way!
|Chris Trice||27/11/2011 11:15:54|
1362 forum posts
Mine has an option to halve/double the Y axis readout too.
|Les Jones 1||27/11/2011 13:03:35|
|2192 forum posts|
If you DRO does not have this facility all you have to do is to configure it by putting in twice the resolution value the scale for that axis actually has. (assuming this value can be set differently for each scale.)
|997 forum posts|
What DRO are you using Stub, i might change.
Will have another try using the Machine DRO 3 axis budget on lathe and mill. Seen it some where but resorted back.
|Les Jones 1||27/11/2011 14:06:26|
|2192 forum posts|
Correction to my last post. I should have said set the resolution to HALF the actual value.
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