Things they don’t tell you in the books so I’m asking you lot

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Things they don’t tell you in the books so I’m asking you lot

This topic has 55 replies, 21 voices, and was last updated 19 November 2010 at 19:31 by Sub Mandrel.

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14 November 2010 at 21:47 #58755
John Coates
Participant
@johncoates48577
Where to dispose of swarf

Have been collecting all my swarf since I started learning in May but am at a loss what to do with it. I try and recycle everything but don’t know if scrap merchants will take it. What do you guys do?

Turning – how to return a RH cut

As I am a newbie I have been getting better with the finish on my turned pieces. But when say RH cutting I concentrate on the depth of cut and rate of feed but once i’ve reached the end of the cut I don’t know whether to return it (a) under power which puts a spiral on the workpiece or (b) with the power off but that puts a cut line into the workpiece. If the answer is to back the cutting tool off, then I never seem to get back to the same setting on the dials e.g. cut at 40 thou, back off, wind back to start, turn feed handle back to 40 thou and the cutter is either not touching the workpiece or too deep, which I guess is the infamous backlash in the slide screw? Can I be saved?

Knurling wider than the width of the knurl wheel

Just tried putting my first knurl on today and it wasn’t great. Got the knurl perpendicular to the workpiece. Now it is one of those clamp types but the workpiece was larger than the tool so the two knurl wheels were at about 7 o’clock and 11 o’clock. I tightened the knurl tool to clamp the wheels onto the piece then turned the top slide feed to advance it into the workpiece. Cut a knurl into the shoulder I had left but it wasn’t very deep even though I advanced the top slide. Then I had more shoulder to knurl but I couldn’t seem to pick up the cut I had done. How do you do it? Maybe I need to but the different knurl wheels (coarse, fine etc)

That’ll do for now chaps! Help your padowan

John
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14 November 2010 at 21:47 #5292
John Coates
Participant
@johncoates48577
Real beginners questions : )
14 November 2010 at 22:35 #58757
Anonymous
Here’s my twopence worth:

Swarf: I doubt the professional scrap metal dealers will be interested in the amount of swarf that a model engineer will produce; especially as it is likely to be mixed up. When I have reasonable amounts of swarf of one type, say more than 50kg, I dispose of it via a friendly local machine shop. Otherwise I take the mixtures to the local council tip, where they have containers for scrap metal. No-one has objected yet, even when I dumped loads of fine cast iron swarf which blew everywhere.

Turning: If it’s not the final cut, I just return the tool while running and accept a fine spiral; it’ll get removed on the next pass. If it’s the final cut I just back the tool out and that’s it. How far do you back the tool out? If you’re backing out by half a turn or more, it would seem that the lack of repeatability is unlikely to be caused by backlash.

Knurling: Are you trying to cut a straight or diamond knurl?

Regards,

Andrew
14 November 2010 at 23:01 #58759
Terryd
Participant
@terryd72465
John,

Scrap merchants in the UK will take Brass swarf in quantity but not Mild steel swarf in my experience. I usually take it (in a Plastic Bucket) to my local community recycling facility and put it in the metal skip. .

Wen turning It is usual to withdraw the cutting tool when returning to the start on the final cut. However It doesn’t really matter otherwise if you have to make further roughing cuts marks will be removed. If you have to withdraw the tool ( I usually do) and you have an indexable collar on your crosslide screw then set it to 0 before withdrawal and withdraw well past the backlash then at the start of the next (final) cut set feedscrew back to 0 and you are ready to put on your final cut. It should be accurate. Make sure that you count the turns of the screw if more than one. Another tip is to make sure that your gib strips are properly adjusted.

Knurling should be ok with the tool as you describe if not perfect. it will take several passes to cut a reasonable knurl in my experience. Do not withdraw the knurl but reverse back to the start with the work rotating but do not disengage the knurl from the work, add more pressure and repeat the process until you get a decent knurl. It is a brutal process utilising plastic deformation of the metal rather than cutting and several passes at the same pressure may be necessary and should be done at the slowest speed possible on your lathe with plenty of oil lubrication, heat dissipation is not a real problem so you don’t need soluble oil for this job. It is almost impossible to get the knurls to register in the original pattern if you withdraw them before you have formed the knurl. It is not an easy process to master. But remember there are many ways to skin the cat.

Try these and come back if not successful for more advice. Others may offer other techniques which may suit you better.

Best regards

Terry.
15 November 2010 at 00:19 #58762
Steve Garnett
Participant
@stevegarnett62550
Swarf from home goes to work, where it goes in with what’s there, although I do separate it as much as possible – the brass gets recycled, but the steel ends up disappearing in a commercial container once a week. OTOH, the plastic is a damn nuisance!

Returning tools – I do what Andrew does.

As for knurling, we had quite a discussion about that a while back – see this thread.
15 November 2010 at 12:34 #58783
John Coates
Participant
@johncoates48577
Thanks guys

Swarf – we have metal and glass collected from our house by the Council but I’ll bet the guys won’t want my swarf alongside the beer cans and wine bottles in the kerbside box! Looks like the chocolate boxes will have to wait until there’s a tip run

Cutting – thanks for confirming that my “spiral cut on the return trip” was something I shouldn’t be doing. As you rightly say the finishing cut is a single pass at the highest speed my lathe can muster

Knurling – will try slowest speed and cutting fluid. As to whether its a straight or diamond knurl I have no idea. This industrial 2 wheel tool is what I bought:

RDG knurling tool

Thanks for the link to the knurling thread

John
15 November 2010 at 12:42 #58784
dcosta
Participant
@dcosta
Hello John.

In the following URLs You can see a knurling tool I made.

It works very well and with I made knurls in almost all materials I work with

without forcing the lathe.

A view of the tool:
http://www.model-engineer.co.uk/albums/member_photo.asp?a=7538&p=146259

Another view of the tool:

http://www.model-engineer.co.uk/albums/member_photo.asp?a=7538&p=146262

An example of work made with it:

http://www.model-engineer.co.uk/albums/member_photo.asp?a=7538&p=144200

Best regards

Dias Costa
15 November 2010 at 12:51 #58786
Wolfie
Participant
@wolfie
OK whats ‘backlash’???
15 November 2010 at 13:30 #58789
Anonymous
Any ordinary screw and nut has to have a certain amount of clearance to work without binding. So, if you’re turning a screw one way and then reverse it, the screw will turn a little bit before the nut starts to move in the reverse direction. Hence the cross slide and topslide on a lathe will have a deadband where the dial turns but the slide doesn’t move.

Points to note:

All manual lathes, even as new, have some backlash

If you’re turning the dial in one direction only then the backlash is irrelevant

If you reverse the dial far enough to reverse the slide movement, and then move back in the original direction to the starting number on the dial, then on any half-decent lathe the slide should be back in the same place irrespective of the backlash

Some bigger, industrial size, machines have backlash adjusters on the screws; basically two nuts that can be moved relative to each other

Some people get their knickers in a twist about backlash – unless the screw (or nut) is so worn that it’s about to fail, you don’t need to worry about it

For reference, on my 30 year old industrial lathe the topslide has backlash of about 25 thou, and on the cross slide the backlash is about 15 thou. It makes absolutely no difference to using the lathe and the accuracies to which I work.

Regards,

Andrew
15 November 2010 at 13:34 #58790
chris stephens
Participant
@chrisstephens63393
Hi Guys,

Re swarf, dump at local tip but try not to look like a business in case they want you to pay.

Re turning, don’t you guys know what a well cutting tool can do? If you don’t, then, what you are aiming for is no spiral on the return “cut”, because the tool is cutting sweetly enough to cut to properly. On the return you might occasionally get an extra polish or as wood workers would call it a “de-nib”. Perhaps David should commission an article on what you should be able to expect, ie surface finish, from various tooling.

Re, Knurling, You can move the knurls sideways while it is knurling to widen the knurled area, the answer seems too simple as though I misread your question. Did you get top slide and cross slide confused?

chriStephens

Edit ,the odd gaps are not there in the original.

Edited By chris stephens on 15/11/2010 13:35:57

Edit 2 think I know what went wrong, so if there are no gaps please ignore edit 1

Edited By chris stephens on 15/11/2010 13:38:38
15 November 2010 at 15:35 #58794
Alexander13
Participant
@alexander13
Re turning – I concur with Chris, that is the way I taught on two different engineering courses one in Shropshire and one in Somerset.

Edited By Alastair Nicoll on 15/11/2010 15:40:16
15 November 2010 at 16:33 #58798
John Coates
Participant
@johncoates48577
Posted by chris stephens on 15/11/2010 13:34:39:

Re, Knurling, You can move the knurls sideways while it is knurling to widen the knurled area, the answer seems too simple as though I misread your question. Did you get top slide and cross slide confused?

No – the top slide was perpendicular to the workpiece on the same axis as the cross slide. They both have the same range of movement (one revolution of the handle = 1/10th of an inch or 100 thou) so I use whichever is the most convenient. For this job with my nose close up by the workpiece to look at the knurling the top slide handle was in the most favourable position
15 November 2010 at 16:49 #58799
chris stephens
Participant
@chrisstephens63393
Hi John,

A curious configuration of top slide you have there. Still, all that matters is you are comfortable with it that way, even though it would not suit all.

chriStephens
15 November 2010 at 17:02 #58801
KWIL
Participant
@kwil
I agree with Chris, what a strange top slide setup you have. If you set it at an angle, you can always advance the cutter by a very small amount, because of the angle, that is you can effectively devide your cross slide dial divisions by whatever you want to put on, say 0.0002″ or 0.005mm. Yes I know it also moves the cut sideways, but you can allow for that.
15 November 2010 at 17:18 #58802
Terryd
Participant
@terryd72465
hi Chris,

Thanks for the tip, I always get a spiral of about 1 or 2 thou when returning my tool except on the light final finishing cut. My tools are always sharp though, The guys in the toolroom when I served my apprenticeship taught me how to sharpen tools using the exact angles for rake, clearance etc for different materials. So I always use the those angles and diamond hone the tools (I use HSS by the way) , before use and between jobs as well as during a job if there are problems. I check the tool is sharp by using it like a Stanley knife to cut paper or card.

The only thing I can think of is that during heavy (very) roughing cuts the tool is very slightly deflected and the tool return is then the equivalent of a finishing cut.

By the way, I was always taught that what you call the ‘top slide’ was the ‘compound slide’ as it can be rotated to various angles. Is that not correct?

Regards

Terry
15 November 2010 at 17:52 #58805
chris stephens
Participant
@chrisstephens63393
Hi Terry,

I never try to hone my HSS tools, as I always seem to round over the edge. I also think that if you use a reasonably fine grinding wheel (100-150 grit ) the very fine striations left by it help rather than hinder a cut.

Now let me put forward my thinking on the difference between heavy and finishing cuts and their effect on lead screws. As we all know there is usually some play in the lead screw and nut combo and this play has oil in it. This oil will act like a little shock absorber, under heavy load it will get squeezed out, but under light load, ie the return cut, it will try to even up the gap and move the cross slide forward. Under a light or finishing cut with a sharp tool the force needed to make the cut will be less than the “sticktion” of the cross slide and the oil film acting together. There is probably some element of bending involved as well as all the other sources of play.

The oil film shock absorber theory then begs the question, should you use thick or thin oil to lubricate your lead screw?

The use of “top” as opposed to “compound” is regrettably down to two countries divided by a common language, ie blame the Yanks!

chriStephens
15 November 2010 at 18:40 #58807
John Olsen
Participant
@johnolsen79199
Well, I have a setup for sharpening that uses a series of diamond wheels, 260, 600 and 1800 grit. After a tool has been sharpened and honed with these it has a mirror finish. They cut beautifully and leave a wonderful finish. However, even these will leave the spiral on the return, which I agree is actually due to spring and clearances in the machine taking up. I don’t think it is especially harmful, except you don’t want to leave it there on the final cut. The dial positions should be repeatable enough to allow taking off the cut and then returning it .

What is harmful is dragging a carbide tip back across the stopped work, as you are liable to leave the sharp edge behind, eg chip the edge of the tip.

regards

John
15 November 2010 at 19:34 #58809
John Coates
Participant
@johncoates48577
Posted by chris stephens on 15/11/2010 16:49:18:

Hi John,

A curious configuration of top slide you have there. Still, all that matters is you are comfortable with it that way, even though it would not suit all.

Aha! Think I know what you mean now Chris

First of all I checked I was calling things by the right name and after checking my Sparey, I am

And yes I did have my top slide in line with my cross slide but then I find sometimes I have to orientate things this way to get the tool in the right position for boring or facing as otherwise the top slide fouls the tailstock as I seem to have a lathe with a very substantial (read wide) saddle

But what I think you mean by “curious” is that my cross slide should be used to advance the cutter across the lathe i.e. perpendicular to the workpiece which is lengthwise between the head and tail stocks, and the top slide set parallel with the workpiece to advance the tool towards or away from the chuck i.e. along the workpiece

Correct?

John
15 November 2010 at 19:55 #58810
chris stephens
Participant
@chrisstephens63393
Hi John C,

Got it in one, or maybe two.

christephens

Edited By chris stephens on 15/11/2010 19:56:52
15 November 2010 at 20:20 #58811
chris stephens
Participant
@chrisstephens63393
Hi John O

There are numerous places where slop can occur, not to mention quality of the original lathe. This is not to say that good wok cannot be produced on the humblest of equipment , provided you know your machine and how to get the best out of it. Obviously the better quality the lathe the easier it is to get good work quickly. On a poor lathe with an unevenly worn cross slide lead screw, good results can be obtained but it requires measuring more often, which adds time to the job.

Earlier today I was modifying some bolts, turning 8mm down to 7, and on the return “cut” there was no evidence of a spiral. Lathe was a fifty year old Bantam and i was using T1200a Sumitomo tips, the final pass took of 0.1mm of DIA ie 0.05 DofC.

For those who say that they have not got time to take such a small cut as a finishing one, and that they would do it all in one and only one cut, I got a finish as good or better than ground finish and I did not need to waste time to “polish” it with emery. I would agree that such a finish was perhaps overkill for the purpose the bolts would be put to, but they look so much better when you give them back to their owner.

Is it vanity to try to get a good finish on all things, or just pride in a job seemingly(?) well done.

chriStephens
15 November 2010 at 22:27 #58817
Anonymous
Surely the surface finish should reflect that required by the function of the part?

Regards,

Andrew
15 November 2010 at 22:54 #58818
Terryd
Participant
@terryd72465
Hi Chris,

I don’t get the rounding problem when honing, I suppose that’s 50+ yrs of practice.

Not sure about the Yanks, My old apprentice trainer who was in his 60’s used to use the ‘compound slide’ term in the late 50’s/early 60’s, as did GHT occasionally. Still, ‘a rose by any other name’, etc.

I agree with you about finishes, I never use emery (all that grit) and expect to get a mirror finish with most steels (and brass and ali) from the tool. I also agree about the final cut, that is never a waste of time, I expect my Morse tapers to be similar to a ‘ground’ finish when I turn them.

If I was just taking 0.5mm cut I wouldn’t get any spiral cut either, even on my 55yr old Boxford, despite it’s misuse in many years of schooling!!, I get the effect when taking upwards of 1.5mm cuts.

I don’t think it’s vanity, just good practice.

Terry
16 November 2010 at 01:51 #58823
chris stephens
Participant
@chrisstephens63393
Hi Andrew,

As a general principle your statement has some merit, but if you get a good finish easily why aim for something lesser. If the size of a turned item is fairly critical a good finish is vital, as you cannot accurately measure a rough surface.

chriStephens
16 November 2010 at 02:12 #58825
chris stephens
Participant
@chrisstephens63393
Hi Terry,

In British English the term is a compound slide, it is the yanks that get it wrong. Please forgive its use here, I have been following too many across the pond sites lately.

If you use just the compound slide to cut your Morse taper, rather than a taper attachment , you might not get quite as good a finish as would if you had used power feed, no matter how good your tooling. If you can, then imagine my cap being doffed.

Re your 1.5mm cut and spiral, Not really surprising, but no harm done. You would have to be supremely confident in the quality of your equipment to take a 1.5mm cut as a final pass, if any degree of accuracy was required. I would not buy any tips that had a 1.5mm DofC as their operating range, I prefer to keep fine finish ones and take more cuts, if needed, but then I do it for fun not profit.

chriStephens
16 November 2010 at 05:10 #58829
Sam Stones
Participant
@samstones42903
I’m addressing John Coates’ second question from the start of his thread dated 14/11/2010 – Turning – how to return a RH cut

As a Myford advocate, I bought my ML7 second hand in the early 60’s. As I recall (from the widow who was selling up), the lathe was brand new in c1946. In other words, this was a machine which had been used for about 60 years when I sold up. It served me extremely well in all the time I used it, although I would have preferred a Super 7 based upon my toolroom experiences.

However, I have to say that, because the design of the ML7 saddle did not fully address the Narrow Guide Principle and issues Kinematic, the inevitable off-set forces, particularly those in opposition from the lead-screw and the tool post, eventually caused wear which allowed the saddle to rotate very slightly in the horizontal plane.

This produced two adverse effects. Firstly, it allowed the cross-slide to twitch out of square, and secondly, upon completing an internal pass, it would cause a tool to remove a little more metal if the saddle feed was reversed without first moving the cross-slide forward and cutter (ie. away from the operator and the work piece). The converse was such that the cutter would lift off an external diameter of the work piece rather than leave a spiral as per the experiences of other members.

By the way, the rectification of this lathe’s shortcoming was the feature of an ME article written, as I recall, by the esteemed Mr Radford of NZ back in the 70’s. He machined (milled) the saddle in such a way that both the front and rear guide faces extended over the full `length’ of the saddle.

As for producing a top-notch surface finish, I adopted the so-called `diamond turning’ technique, ie. by stoning a tiny flat in the tip of the cutting tool. This flat would be absolutely parallel with the direction of travel, while being slightly wider than the feed pitch. You can imagine that this would virtually eliminate any evidence the the feed!?

Regards,

Sam
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