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Member postings for Martin Dowing

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: New scam to beware of
02/12/2020 10:42:13

With all similar "enquiries" my SOP is to say "no I am not interested" and bang a phone.

Thread: Workshop temperature - cold
01/12/2020 14:05:48

My garage is warm, with central heating.

Nothing rusts there, even my wife is happy to sit there and observe how swarf is made.

She is very fascinated while watching it, very much like neighbours cat which often comes and also watches.

Welding and rough grinding are always done outside, on free air.

There is wooden bench in garden for that.

Thread: The Old One - Broken Tap Removal?
01/12/2020 06:32:52

IMO there is no prospect of success with selective dissolving of tap.

Go to shop with EDM facilities. They may help if sympathetic to your plea, time permitting.

Thread: Thread cutting problem
30/11/2020 22:13:27
Posted by Buffer on 29/11/2020 17:04:44:

thanks again to everyone who has taken the time to reply with advice.

I did what Andrew suggested and cut a thread perfectly on a piece of 3/16th brass. So there is nothing too wrong with the die it would seem.

I managed to cut a thread in steel but only by taking the bar down to about 0.18 but it didn't look very nice. It seems that despite me pushing the die towards the chuck it just wouldn't start pulling itself forward along the bar and it appears to just grind the steel away until it can get going and then it pulls itself along. So I did what I didn't really want to do and set the lathe up to screw cut. In the end I managed to get a very nice test piece cut on the other end of the brass rod so later I will try it on the steel.

It is common for die to cut well on brass of nominal diameter but on steel only on slightly undersized bar.

From my experience 2-3 thou undersized steel bar is getting threaded very well.

I have M10 die where manufacturer have stated that steel bar to be threaded must be 9.85 mm of diameter!

Of course die must be pressed square. Proper holders are best but some shabby settings employing pressure of tailstock barrel for squaring while starting your thread also can work in absence of holder.

Thread: Problem slot milling in lathe
30/11/2020 21:48:52

@Gary Clarke.

I have ML7 and I have done plenty of milling on it.

Despite of what people say, once enough thought is given, very reasonable milling cuts can be achieved on this lathe.

My current record is a beautiful, clean 14 mm deep cut done with 10 mm wide circular disc cutter of diameter 63mm held between centers. It was done with single pass on 45 HRc steel bar 40mm diameter, to make a slot across it, with an aid of vertical slide.

My guess is that holding your cutter in chuck is a cause of problem as long as lathe bearings are fine.

Old chucks are tending to be bell-mouthed and cutter is also kept far from bearing. Not good.

You should buy MT2 mill holding chuck with ER 10 or ER 32 sets of collets and for smaller mills use Myford collet system which is very good too.

Always drive your job into a mill in such a way that mill is not "dragging" it on due to feedscrew backlash and that cutting force is taken by machine headstock rather than bearing caps.

Always lock unused slides as others have pointed out.

Thread: Taper turning
30/11/2020 17:14:47
Posted by ega on 30/11/2020 15:55:1

I recall that GHT said he would be unlikely to want to move his Myford TTA from its position and that he made a cover to protect it from chips so that it could remain there semi-permanently.

My is fitted permanently.

I did not find falling chips harming it at all and it helps to place clock used for example in alligning work in 4 jaw.

Once oiled it will not rust either, albeit my machine is in nice, warm garage and nothing rusts there.

All what I need for taper turning is to remove feedsrew from crosslide and then connect attachement with crosslide.

30/11/2020 17:03:53

For my ML7 I have bought original one from Myford on ebay and it works.

Several years ago have paid 300 queeds, so not too bad but not cheap either.

Second hand one is very good, because these are hardly ever used.

The only real use where it is irreplaceable is making accurate internal tapers.

Otherwise it is best to buy or make "tailstock set over attachement" or use boring head mounted in tailstock instead.

I assume one hates meddling with setting over tailstock itself due to hussles with re-allignement for parallel turning.

Thread: Tool for rounding and edge of metal plate
27/11/2020 19:23:24

@Jason,

Have sent you pm.

27/11/2020 18:58:28

@Jason, I have measured original part which need to be replaced.

Radius there is 7.5mm so we have 15mm diameter, however I have inserted it to the pump to observe how it works with its mating surface.

Base on this I am confident that 8mm radius will also do as good as original and 6mm one should work as well.

However a bit larger one should improve seal, so I went for 8 mm.

Maximum radius there which should still work is in range of 10-12 mm.

Any larger and sharp corner of slider would start scratching bore of pump during rotation.

If you are interested I can post photo of parts of disassembled pump and it should be obvious for most how this pump works (it is rotary vacuum pump with eccentric running spindle working in oil).

Edited By Martin Dowing on 27/11/2020 19:00:05

27/11/2020 18:46:57

@peak4,

Yes, Chinese company which cannot be mentioned here for some reason and which I easily found on Aliexpress is selling very decently looking and also cheap solid carbide radius cutters up to 8mm radius in increments of 0.25mm, so there is a very wide range offer of them.

27/11/2020 18:39:08

@old mart.

Have already ordered solid carbide one of radius 8mm from China. Cheap enough.

Rated up to 50-55 HRc.

Just getting advice how to use it properly.

27/11/2020 17:25:28

@Hopper,

My stupidity, sorry. 15mm is diameter.

27/11/2020 10:21:08

John,

I have Myford dividing head with overhead bar serving for tailstock so I could do it.

But these cutters are cheap if bought from China.

So why not to try?

27/11/2020 09:36:14

Jason have made correct drawing of what I want to make. Sadly I don't have access to autocad/autodesk software to make such a nice drawing.

@Jason,

You can round corners of plate on lathe as long as radius is such that similar plate could be made by milling round barstock. Unfortunately it is not the case in my situation.

These cutters are cheap.

HSS variete of 8mm radius you can get from China for $10 and solid carbide version below $80. Free p&p. Shank is 20mm so ER32 collet of this size will do.

Those for 6mm are twice cheaper with 16mm shank.

So would you go for 45 deg angle and a single pass?

My plate is 6mm thick mage of 6mm steel gauge plate, 45HRc (Toolox 44).

@Henry Artist,

This will be a slider used in quite elaborate spindle of rotary vacuum pump.

Edited By Martin Dowing on 27/11/2020 09:38:46

Sorry to edit your post but the supplier linked does not meet the code of conduct conditions on the forum

Edited By Mike Poole on 27/11/2020 09:50:31

26/11/2020 21:54:08

I need to round an edge of metal plate (45HRc) to precision radius of 15mm.

Because plate is wide turning is out of question.

The obvious idea is to use dividing head with tailstock to mount said plate and patiently proceed with inching bit by bit and taking straight cuts with end mill, then smoothing radius so produced with sandpaper etc.

There is also a simpler method:

One can buy corner rounding end mills which are essentially "inverted form of ball mill"

I can envisage 2 ways of using them.

First would be to use them perpendicular to plate, make a cutting pass, invert plate and make yet another pass (there will be witness mark for sure and other issues with geometry calling for careful machine setup.

Second way is to set end face of plate under angle of 45 deg to the axis of mill and proceed with a single cut.

This looks like the best way to proceed but could you comment on it?

Thread: Carbide mills on slow spindles
02/11/2020 21:37:03

So what is wrong with solid carbide stub drills with sharp point? They look like regular twist drills but have a sharp point and are ground to 90 or even 60 deg angle.

This pointed end is so easy to chip off that I don't even know how to use them without breaking them.

This was discouraging me from using other carbide drills and mills for quite a while.

02/11/2020 15:55:27
Posted by Andrew Johnston on 02/11/2020 13:28:50:
carbide inserts for turning and milling often need minimum speeds, depth of cut and feeds to work properly. But the same is not true for "solid" (*) carbide cutters.

These are good news for me. I don't have much troubles with carbide inserts. They are running well on my machine including those from boring bars for indexable inserts while drilling 15mm holes and 40mm end mill for indexable inserts which can take 4mm cut in cast iron with a little squeaking but nothing chips.

I have broken sharp tips of solid carbide stub drills though and this observation was discouraging me from trying carbide mills.

So I will give a go for my new carbide mills. Maybe they are going to work and my problem was a bit psychological in nature.

Mind you, whats wrong with these sharp pointed carbide stub drills that their tip is getting broken so easy?

@Oldiron,

Very often it is impossible to find out what Chinese guy will sell you before you get it.

OK, HSS you can recognize by photo but if you are offered TiCN coated end mill described as "hight speed tungsten steel" selling well below a price of regular HSS here you are not suspecting that carbide will come.

Mind you, these mills are of rather high quality as determined by guy with big rigid machine.

02/11/2020 12:22:14

HSS mills are increasingly replaced by carbides and it may not be long before they are not easy to get, particularly those smaller diameters.

Yet if you have a slow spindle (my will go up to 1250 rpm) then carbides are not really good as they chip easy.

Even 1/4 inch carbide need something like 2500 rpm to work efficiently.

I have tried to buy 1/4 inch HSS bits from China.

I found an offer specifying $5 each, so got few. It was described "high speed tungsten steel" and you guess... carbides came.

Any ideas how to make intelligent use of them on slow spindle?

How fast plain bearing based on phosphor bronze and hardened spindle of 1-1/4 inch diameter can run?

My friend have tested one of these carbide mills at 3000 rpm on mild steel and it works really well.

What is a slowest rpm at which such 1/4" carbide mill can run without excessive risk of being destroyed on both mild steel and stainless?

Edited By Martin Dowing on 02/11/2020 12:40:15

Thread: Reaming hole in 45HRc steel
02/11/2020 06:04:52

Thanks for these comments.

With solid carbides I always have reservation about possible breaking of drill or mill in my workpiece, That due to rather low speeds of spindle at my disposal (up to 1200 rpm).

So if carbide has to be used then brazed versions are preferable in my case.

Regarding EDM - dont have it..

Thread: Change gear alternative material
30/10/2020 22:15:55

If anyone wish to cut gears of Tufnol then it is plate and not bar what is a suitable material.

Gear made conveniently from bar won't last long.

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