Member postings for Martin Dowing

Thank's all of you for comments. So after all there are ways to lap tapered parts.

@Michael.

Reciprocal linear movement of tapered mating parts while maintaining full contact is impossible, so abrasive cannot be distribued like in lapping of cylindrical parts and it will tend to accumulate forming groves etc.

It is well known that lapping of tapered features does not work but what about honing?

Lets say that we want to hone a bore (or an arbor) using 3-legged hone applicable in motor industry. For honing an arbor of course spring would be rearranged in such a way that honing stones are grabbing tapered bar rather than springing out.

With steep tapers there would be a problem with rapidly changing force of contact because of changes of spring tension along a taper and that would cause slight changes of taper angle (not acceptable).

But what about mild tapers, say one of 1:50 or even a taper like MK4?

Did anyone try that and what was a result?

Edited By Martin Dowing on 19/02/2021 20:49:16

Leadscrew you can buy from McMaster Carr (LH, 5/8 inch).

You can buy 3 feet section.

Feedscrews you can turn yourself. Do it from 40-45 HRc rod and they can work with phosphor bronze.

ACME taps Chinese are selling cheap so nut is not a problem.

ACME nuts together with section of screw they also sell. They are cheaper than p&p alone from most of Western dealers.

You may adapt Chinese ACME screw by turning and threading ends and brazing thrust collar.

Leadscrew half nuts are best poured out of white metal.. Use secttion of leadsrcew as a form.

You will need to process ends though albeit it gives you good opportunity o install shear pins as gearbox protection.

Martin

I have done many details from this material.

Have found it quite pleasant to work with, it gives nice surface finish ex knife unlike many lower quality carbon steels (BDMS comes to mind...)

I have only a small lathe (ML 7) yet I can make 2.5mm cuts at 0.004 inch/rev on 40-60 mm bars of it with normal front tooling. As long as HSS is sharp no trouble is observed. Small Chinese 6 mm carbide inserts worth 0.3 queed each are doing real wonders on this material and they are lasting long. With carbides I cut dry, with HSS I use paintbrush cooling.

When drilling, drill must be sharp or it *will* work harden indeed. If it does work harden during drilling then Ghinese carbide spot drill worth few queeds and designed for 55 HRc will invariably resolve problem. Nevertheless *sharp* 16mm drill may be applied directly with no predrilling and it works well.

Parting must be done with sharp HSS tool or it doesn't work at all. 35mm bar have been parted off in my ML7.

I have made 3-1/2 inch deep, blind bore in 100mm diameter piece of this material held in 4-jaw. Taken some time but result was very good indeed.

Martin

@oldvelo,

I think, I misunderstood you.

Do you mean belts like those used for example in washing machines?

I have hardened (60HRc) bars which need to be ground between centers.

They have holes at their ends but these holes are 90 deg. with normal pilot hole drilled deeper so there is no risk of center tip hitting a bottom..

Can these be ground between normal 60 deg. centers on cylindrical grinder?

I need to make slight 2 deg taper on these bars and I wonder if shop with a grinder will fret about these "wrong" holes or not?

@oldvelo,

System will be used for motor speed reduction, so sizes of pulleys have to stay as designed.

Smaller pulleys are already rather small and further size reduction would only bring unnecessary strain..

But yes, I do use poly-v belts because they perform so much better.

Martin

I think 5 people should be enough.

1 is standing on table and holding the bulb and 4 are turning a table around.

Unfortunately 2 additional people are usually required, one from HSE to supervise what engineers are doing and one to report on the forum what have been done.

So we have 7.

Wait a moment... we forgot about 2 guards necessary to watch out, so electric current does not escape.

So 9 are needed.

Thanks for all your comments. I will go for 36 deg., not exactly what industrial art calls for larger diameters (38 deg) but more than usually modellers are doing (30 - 32deg).

Reasoning is that pulley will be used quite a lot but because it is going to be made of aluminium, then this angle will be a little bit steeper to accomodate for wear.

Martin

I need to make rather large pulleys (140-200mm) for standard 10 mm V-belt.

Grove is to be 9.7mm wide on the top and 11mm deep as theory and published projects are saying.

What are correct grove angles?

What I have found that tor a small pulley (up to ~3 inches) correct grove angle is 32 deg and for larger pulleys it is 38 deg.

I understand it, as it seems logical that due to larger contact area of big pulley frictional force per unit of contact area does not need to be so high because total contact area is larger.

I am aware that many people are making pulleys with 30 deg angle, regardless of size.

So what is correct angle for large pulleys?

38 deg or perhaps less?

Suggested something what is of more use than just making a bar more narrow. Accessories are critical and Myfords series have plenty commercially made.

Re Safety - quest for perfect safety is a disease digesting our society which is ensuring that nohing can be done and Asia takes over everything.

When I was 12, I didn't have a lathe but have learned in my uncle's garage to operate oxyacetylene burner quite profficienly (he was handing me down some works...).

What is safer, lathe or such a burner, I don't know. Even acetylene needed to be generated from carbide and I was operating generator as well...

Of course in initial stages kid would need to be supervised but after 2-3 months less so.

Edited By Martin Dowing on 14/02/2021 23:00:44

If you can set aside about £ 3000-4000 and have a spare area for a workshop then buy him some second hand lathe like Mayford ML7 or Super7, together wih accessories like vertical slide.

You will find plenty on offer on ebay and elsewhere.

Consult someone experienced (ask him to inspect this lathe before you purchase) and ask him to set it on.

Plenty of knowledge can be found on internet (and your son will find it easy) but before he has made his first steam engine it will likely be few years of skill learning.

He must be *patient*.

Amateur engineering / precision mechanics requires lots of *patience*.

We are often spending many days to fabricate a single part.

This hobby is not cheap either and your son will unlikely make any money out of it unless he has acquired some very special skills or found a niche or unless current edition of civilization together with high volume manufacturing have collapsed.

West is essentially done - even multimillion engineering ventures are struggling and increasingly failing while competing wih Chinese.

Edited By Martin Dowing on 14/02/2021 21:36:53

About 10 years ago one guy have repaired a vice with dovetail cracked very much like your..

He just painted it very well and sold it to me. I have never seen him again (car boot sale).

@Gerhard Novak,

Don't tell me hat you made all of that in a single day...I feel intimidated.

I have managed to make a dieholder for M10 die as an addition to my usual set used on ML7 tailstock.

I will tend to suspend an item in vapors of boiling organic solvent like acetone or butyl acetate (used as paint thinner) if good degreasing is required.

Some solvent on bottom of pot, item suspended on net, pot covered with stainless bowel filled wih water - ir works as reflux condenser. You may use water - ice slush for better efficiency.

But boiling with concentrated sulfuric acid - no way.

Concentrated sulfuric acid boils over 300*C while giving off obnoxious, corrosive white fumes and accidental spill on your body of larger than minute quantity will leave you disabled if not dead.

You can slightly warm (50-70*C) your slide with conc. sulfuric acid containing some chromium oxide or chromate followed by soaking in distilled water and finaly in glass distilled solvent like methyl or ethyl alcohol - much safer, but I doubt that many alloys would take initial step without corrosion.

Trouble is that chromates are not easy to secure for private use these days and need proper disposal.

If these screws are small then Jacobs drilling chuck or other small chuck installed on MT2 taper shank can be used with a good drawbar and said drawbar should preferentially have LH threads, albeit unlikely failure of normal setup is rather inconsequential - it will get loose but usually stay in place long enough to react.

An alternative is a Myford collet system, one used to screw on the spindle nose as it can handle up to 1/2 inch and 13 mm.

Tightened with a tommy bar such collet will *not* undo and even if it did by miracle, it is also inconsequential.

Screwed on chuck in reverse is not in my cooking book at all for other purpose than undoing stubborn chuck (on backgear).

Also ML 7 have thrust bearing designed to take pressure of cut in normal R-->L operation.

Operated another way will rely on thrust collar what can be occassionally done but it is not a recommended procedure.

I will tend to operate my ML7 that way while making LH screws (of course spindle turns in normal direction during such exercise).

I am not a safety maniac at all and sometimes work in a way which would cause a heart attack of HSE official but common sense is telling me not to run ML7 or any other lathe with screw on chuck in wrong direction... Neither keeping your eyes in firing line of tool, should it get broken, or meddling with long swarf while machine works is a good idea.

But it is your lathe, so do what you see fit... You may get away with a lot while your lucky star is shining on.

Edited By Martin Dowing on 12/02/2021 22:44:46

Indeed.

Even with 5 thou taper along bedways you will pass by.

ML7 specifications are allowing for 3 thou per foot taper and ispector in the past would pass such machine.

Wear near headstock often leads to minor tapers on jobs held in chuck. Something like 1 thou per inch on occassion, however on longer jobs you do not observe "proportional taper" developing. Without returning shears to parallel condition (scraping of inner vertical surface of the shear near you) not much can be done about it.

In such a sad situation you need set of gauge blocks to measure distance between shears accurately parallel reference slab, scraper and some patience - not that difficult.

Also you may adapt until now unused back shear as a guide (you need to make a gibstrip for that).

You should look for wear of bedways, carriage, cross and top slide, check all gib srips, make adjustments as necessary.

1 thou of play on headstock bearings is also quite much. I have not more than 1/2 thou on my own ML7. When bearings are adjusted properly there will be no play (oil film is not compressible).

You may wish to clean bearings and spindle from all oil using petroleum and then check what your *real* play is.

If you get 3/4 up to 1 thou in "wiggle test" run that way, your bearings are fine.

Otherwise there will be shim adjustment or/and bearing scraping.

You also need o check for an *end play* of your spindle as that is a common reason of chatter (if found it is easy to correct by tightening screwed ring on the left side of spindle but do not forget to untight grub screw in that ring before doing so).

Making an old ML7 working as new and better is a never ending project. I have my ML 7 for ~20 years, refubished it from a scrap like to "as new" condition and have done plenty of upgrades. So bedways and mating surfaces were scraped in, headstock alligned (easier than many think - there is much of false mythology that it can only be done properly in factory setting), spindle and bearing replaced for phosphor bronze and hardened version, countershaft remade from hardened material, one of worn pulleys remade, oilers remade, tailstock barrel first remade but then I got S7 tailstock and now this one is used etc.

And of course old, not hardened spindle was not thrown away at all. Former owner have damaged tapered socket by boring it parallel (lathe crash) but for one job this spindle have proven invaluable.

When I needed to process ends of new precision leadscrew for my ML 7 purchased from McMaster Carr I have reinstalled back my old spindle for few days and damaged tapered socket *just* allowed to pass new leadscrew through the bore.

You will learn a lot of fitting art while proceeding with all such works.

Modern professional guy who operates CNC and nothing else may well look with envy on your skills after few years of such practice.

So good luck!

Martin

Edit:

Regarding "test bar with bobbins".

I have taken a 14 inch section of 20mm diameter hardened linear bearing shaft (they are cheap these days) and locited in 2 of 1-1/4"  phosphor bronze bobbins on such a way to get a distance of 12 inch distance between them. They are turning very nicely without any chatter and measuring is pleasant and straightforward.

Martin

Edited By Martin Dowing on 12/02/2021 09:03:28

Ramon,

OK, I will settle for aluminium oxide "fine" lapping paste and a lap made of copper pipe.

If there are any troubles I will move to fine grades of silicon carbide.