Here is a list of all the postings Martin Dowing has made in our forums. Click on a thread name to jump to the thread.
|Thread: Drunken pulley|
@not done it yet.
It was left in my dad's shed and forgotten.
Seen daylight again only recently.
Other pulley fit on this shaft doesn't wobble but I need this pulley for something else.
Pump was not used for very long time, possibly for 40 years, so I will have to test it after running it for an hour or so.
But thanks for your remarks. There is a belt guard, so it doesn't annoy my eye once covered.
Thanks for comments, all of you.
It is also very annoying for me and I will bore hole and install a bush like all of you are suggesting.
I will fit bush easy - have access to liquid nitrogen if needed.
Tried few times and interference fit is very nicely made.
Loctite or that. I am considering loctite because pulley is made of cast iron and interference fit could crack it.
Pulley is not from lathe. Just 50 years old pump. There is a belt guard so it would not be seen while working. Still very annoying.
Edited By Martin Dowing on 15/04/2021 19:56:33
I have one old machine which has a pulley problem.
Hole for axis is not true to tthe plane on which transmission belt works and this results in wobbling.
Pulley works with V-belt and has 5 inch diameter and a "total runout" of wobble is 2mm (~1/12 inch).
Distance between centers of both pulleys is 10 inches and second pulley has a diameter of 1-1/2 inch.
Quite annoying situation.
Would you leave it as it is or repair faulty pulley by drilling larger hole, soldering in or loctiting core and drilling it again?
Does such a wobble affect bearings causing faster wear or can it be ignored?
What about expected wear of transmission belt?
Many thanks for any comments.
|Thread: What Did You Do Today 2021|
Few more photos:
From time to time I was busy with repairing rotary vacuum pumps for a a guy who is servicing these.
This was usually involving making stellite ball valve seats to work with ceramic balls.
Such valve is virtually indestructable.
Hovever I got one small old fashioned pump which had spindle damaged and was completely naked.
He gave it to me as "irreparable - do with it what you want".
So I have enlarged damaged working bore a bit (turning and honing), made from scratch new spindle which is of very interesting construction, made sliders which fit into a slotted section of spindle, replaced valve seats and balls as usual into stellite - ceramic set and pump was assembled.
Also bearing bore was lapped and a flange used for bolting of pump to its oil tank was repaired by welding.
So really I can say that I have made new pump from castings.
Spindle and sliders were made of 45 HRc material.
Already tested and it easily goes down to 0.01 mbar - pretty good.
Taken quite a while to make it - few linear dimensions had to be made up to a single thou tolerance.
Edited By Martin Dowing on 18/03/2021 21:42:51
Edited By Martin Dowing on 18/03/2021 21:49:03
Edited By Martin Dowing on 18/03/2021 21:51:24
|Thread: Flat bottomed hole with a boring bar - technique?|
Lathe set to produce tailstock end of bar larger in diameter than a headstock one will also produce Morse socket like bore at opening with front tooling and it is a preferable situation if piston entering bore meets gradually increasing resitance (easier to rectify) than large resistance at he entry followed by dropping in a bit further down a bore.
About these and other practices (including up to 3 thou taper per foot) i was told by a guy who was working few decades in Myford, N'gham, while it still existed.
According to him ML7 with 3 thou a foot of taper would still be passed by inspector albeit most of assembled lathes were doing much better than that, typically ~ 1 thou a foot.
Perhaps discrepancy of our data is related to bed straighness versus assembled lathe straightness.
Edited By Martin Dowing on 13/03/2021 17:09:06
There is someting like 0.5 - 3 thou per foot taper.
Myford specificaion says about "up to 3 thou per foot".
It is usually "less" but inspector would pass such a lathe as well (my is turning a taper about 0.5 thou per foot).
This taper is set in such a way that diameter of turned bar increases towards tailstock.
This implies that hole turned with front tooling would resemble lets say Morse tapper (of course not near this steep).
With rear tooling the opposite is true.
Lathe which would turn bar *narrowing* towards tailstock would be sent for rebuilding (headstock re-allignement) by inspector - not acceptable.
Comparable rule applies with facing - lathe is designed to give slight concavity with front tooling.
Slot drill does not produce FB hole.
Bottom is going to be convex.
OTOH boring bar will produce such an animal (or something very close to).
I would go around a problem presented by OP by frist relieving taper with sharp tool, shallow cut going down to bottom and then facing bottom with boring bar and final 2-5 thou cut while boring bar is retracting.
It can also be found (at least on my lathe) that truly parallel hole (or somehing very close to one) is produced by inverted bar cutting on wall farther from operator.
Normally such a hole would have lower diameter on entry than on the bottom (assuming lathe is set properly, eg to turn bar in such a way that diameter grows towards right end of bar).
However minute deflection of bar is compensated for by doing so and hole ends up parallel with carful, shallow finishing cut.
Edited By Martin Dowing on 12/03/2021 23:50:21
|Thread: What is running-in oil?|
I didn't try it yet, but I have been advised on this forum that abrasive pase which wears itself and breake down fast and can be run into mating parts *does* exist and it is called Timesaver(TM) lapping paste available in the UK.
So maybe try that as a small additive?
I would like for someone more experienced to comment on that though.
|Thread: Machining phosphor bronzes|
Many thanks for all your comments.
Will try your mehod of drill grinding next time.
Yes, that was my phosphor bronze - very much like material you describe.
Interestingly turning and parting off, very much like boring is rouble free.
It is drilling what is problematic.
Did you or anyone else have tried to tap this material btw?
Also many thanks for comments of some of you that "small pilot hole is a good pilot hole" and Neil's remarks about usefulness of predrilling in such situation in general.
Some of them are nice and others are pig.
I got one difficult sample.
It turns well to a nice finish, will part off and drill with small (up to 5-8 mm drills).
However drilling with larger drills or slot drills ends up in failure, regardless how sharp they are. Regrinding doesnt help either.
I predrilled 8mm and tried to open up bore up to 12 mm and this was of most horrible drilling experiences I ever had, even if successful after long struggling.
Drill just doesnt want to cut and that's it.
It is not a very hard material either but now I better understand why it is so good for bearings.
Do you have any ideas why it behaves so or know tricks around it?
|Thread: PTFE Rod|
Dust like dust - not good but not very dangerous either.
What *is* important is to avoid smoking while machining PTFE.
Dust go to cigaret, undergo thermal depolymerization and very toxic gas known as perfluoroisobutene is formed.
It is about an order of magniude more toxic than phosgene, and even very small quantities can make one very sick or kill.
Canaries are dying in kitchens where housewives are carelessly using PTFE coated frying pans for a good reason.
|Thread: Inherited ML7 in need of some love - where to start?|
When I got my ML7 about 17 years ago first job done was stripping it all apart, washing eveythyhing with the exception of bed and electric motor with petrol by immersion. and washing bed with petrol soaked rugs.
Because paintwork on my machine was damaged badly I have stripped all of it from bed and all parts with the eception of those made of aluminium which were OK.
For bed (after intelligent protection of bedways and other machined parts etc) sand blast was used, everything else was done with drill/angle grinder & wire brushes.
Attention was paid to detail in removing old paint from all corners and hidden places - quite perplexing
Then all parts ready to repainting were washed by brushing under immersion in isopropanol and dichloromethane. This time bed got the same treatment and only motor was cleaned with rugs.
Then epoxy based industrial paint applicable in mining industry and not available from shop to public was used immediately according to manufacturer specification.
Immediately - to prevent flash rust.
Being chemical engineer I don't have problems with that.
Then machine was reassembled and many things including bedways, saddle etc was rescraped. One guy from trade who has biax and is profficient with i done it for me.
Gib strips were replaced too.
Then spindle and damaged bearing was replaced into phosphor bronze version and then machine became usable.
Much more was corrected as time pass and now my lathe keeps specifications as new.
At that time Myford (Nottingham) was still operational, so many spare parts I got easy and of good quality.
So really my ML7 started as a set of castings.
Edited By Martin Dowing on 03/03/2021 21:43:28
|Thread: Metric feedscrews for ML7 /S7|
I will rather need to cut it.
It is bent across threaded section and badly.
He dropped something heavy on it.
I will only need to find a way to find if it is 29 or 30 degree angle.
Standard metric sizes of trapezoid screws are 8 and 10 mm @ 30 deg.
At 9.8mm you would have a point, but at 9.56 - unlikely.
I have an original imperial 3/8 inch / 20TPI ACME feedscrew made by Myford (Nottingham). It has diameter exactly 9.52 mm.
Applying your logic it should have diameter 9 - 9.1 mm.
With micrometer (Starrett 0-25mm), across threaded section.
Thanks for this comment but I would not take a risk to test click it to find out for sure.
I bet they would find one facing such opportunity.
Edited By Martin Dowing on 02/03/2021 09:27:53
I have such metric screws on my machine for a long time and there are no issues with them.
When I made an upgrade to long cross slide and "modern" looking top slide long time ago I got it all in metric forms.
However my friend brought to me damaged (bent) metric feedscrew from his topslide and asked me to make duplicate.
Then I have started measuring and found something weird - mixed metric - imperial design.
Myford sells them but they are calling close to 1000 quids on ebay (!!!) and anyway "new Myford" stuff usually is not really a match for original parts.
Once I have ordered myself replacement tailstock barrel and it came with badly scored 2MT socket, damaged as new.
After complaining they replaced it but meantime I have made one myself, even better in quality than what they sent and also made of 45 HRC material but with only short section of ACME thread - suitable for lever operated tailstock.
@not done it yet,
3/8 inch for certain, angle is still not 100% certain but rather 29 than 30 deg.
Thanks for these comments - they make good sense.
I got damaged metric feedscrew for Myford ML7.
It looks like it is 3/8 inch diameter 2mm pitch 29deg ACME screw.
Am I correct?
It looks like this screw is of mixed metric - imperial design.
Does such a screw exist at all in standart engineering charts?
|Thread: Worn saddle fix. Is this a bad idea?|
I am aware that many people done what you describe, usually with success.
But why not to scrap back to shape original guide or/and a lathe shear as necessary?
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