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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: Countersink bits
27/02/2021 16:13:26

There are *asymmetrical* countersinks where 3 segments with cutting edges are at different angles to each other.

This design is implemmented explicitly to reduce / prevent chatter.

Martin

Thread: Indexable tool insert replacements
26/02/2021 23:56:33
Posted by old mart on 26/02/2021 19:52:29:

Just buy the cheap ones and don't forget to get them for aluminium, usually labeled H01. For hobby use they are very good.

If you want to pay more, but don't want to buy inserts in boxes of ten, then check out APT, they sell a selection of singles for hobbyists, and their laydown threading inserts are always available singly.

I am only purchasing CBN inserts in quantities lower than 10.

All inserts for general work I was buying in boxes of 10 for some time until one particular type was identified as outstanding.

At this point I have negotiated with Chinese manufacturer and purchased 1000 of them at very significant discount.

They will probably last for rest of my life, I believe, so issue of " general purpose good turning insert suitable for ferrous and many nonferrous alloys which gives good finish and last reasonably long" is probably setled for good.

Cannot say which particular Chinese brand it is and from whom it was bought due to forum policy but inserts are really good indeed.

26/02/2021 09:49:15
Posted by David Jenner on 26/02/2021 07:33:07:

I'm at the point of needing to replace the inserts on my lathe tools.

I have identified the sizes:

CCMT060204, DCMT07204 and TCMT1102.

My question is "what is the difference in brands?"

There seems to be a huge range of prices for what seems to be similar tools.

Interested to hear peoples views on this.

Dave

From amateur perspective whatever you buy will sereve, one short time, another for longer.. Chinese inserts from Ali, particularly if you don't go for the cheapest are of outstanding quality these days and together with postage they cost chaper than p&p from European manufacturer.

I have bought two handfuls of these @ $0.2 each. Free p&p was offered. Outstanding quality, in various tests run up to 1200 rpm they perform as good as Sandvik when used for stainless. Should last for life.

Thread: Magnetic v-blocks - how useful these are?
25/02/2021 23:18:52
Posted by Nigel McBurney 1 on 25/02/2021 15:13:55:

I have had a Mitutoyo magnetic vee block for 30 years,I rarely use it,the snag I found was that if you want to drill a cross hole in a shaft on a drilling machine,a centre pop on the shaft is set central by eye,then the mag "on" lever is operated,thats ok it holds the work resonably securely but the magnetism in the base stops the block being slid around on the drill table to get the centre pop under the drill point,I prefer an ordinary vee block,if precision is required then its either use a vee centre in the lathe tailstock or on larger round bar work its a machine vice on the vert mill set up central using a wobler tool.I have three sets of paired vee blocks ,plus a very precise Bilton single block and an Eclipse toolmakers vee vise. Though they all suffer with the snag of the drill chuck can hit the clamp on occasions. I do have a pair of old Verdict v blocks which have the an arrangement of slots on the sides of the block which contain the clamp so if the block is laid on its side the clamps do not foul the surface plate or drill table,My mag vee block came "free" I would certainly not buy one.My pair of Eclipse hardened steel vee blocks,are now 60 years old very expensive in those days bought at a small discount via the company apprentice tool scheme,though still in excellent condition.

Nigel,

I have made myself a simple device (precision ground bar with 2 holes precisely crossdrilled & reamed 4 inches apart and exactly through center).

This allows me to set vee block exactly at centerheight and parallel to lathe bed (short section of precision rod hold in collet must pass without any resistance through these crossdrilled holes - made to h6/H7 fit.

Vertical slide is manipulated to achieve that.

Once done you are ready to for cross drilling. Setting milling machine would be comparable.

25/02/2021 23:02:40
Posted by herbert punter on 25/02/2021 10:16:44:

If you believe that the terms ‘indian’ and ‘precision ‘ are mutually exclusive, it may be interesting to look up Jantar Mantar, Jaipur. I went there a few years ago, and was very impressed.

Bert

I am aware of story from Myford (Beeston; N'gham) - they have ordered from India collets for ML7/S7 lathes - they had to be returned because specification was not met. So Indians made a new lot - also had to be returned.

This was long time ago. More recently I have purchased rotary table from Indian conpany - it was simply unusable.

Rotating part of this table was simply "wiggling" in its housing. I had a lot of troubles to make it working (remachining and loctiting of processed precision ring from bearing made a trick, though CBN insert have gone damaged in the process).

But it is a large country so surely somewhere must be few companies which are keeping good standard.

Anyway, many thans for comments all of you.

It seems o be useful device.

Thread: Skynet is Coming
25/02/2021 20:51:08

There is no need to connect discussed devices to wifi and their smart functions (IoT) remain dead.

Up to now I have none of these and pay attention not to buy any.

I don't want my fridge to report me to taxman, should a total amount of stuff taken in and out during a given month exceeded certain proportion of my pay.

Real troubles will begin once you simply cannot run these household devices without internet connection.

There might be a new profession for electronic geeks on horizon:

Disabler of smart functions.

Thread: ML7 Hand Crank / Wheel?
24/02/2021 20:48:41

There is a genuine Mayford accessory meant exactly for your envisaged jobs and it it called a crank.

I have bought it direcly in Myford works (Beeston) while factory still existed.

It can be installed easily and tightened by means of split mandrell and tapered cone.

It can also be released easily, all done in seconds.

I am using it with every success and it is really handy for example for setting job in 4 jaw with an aid of clock and it is holding strong enough to tap M12 in steel with no problems.

Thread: Magnetic v-blocks - how useful these are?
24/02/2021 20:29:21

There are on offer on ebay Indian magnetic v-blocks. Cannot include url because it is very long link and I don't know how to shorten it.

Of course words "Indian" and "precision" does not mix well but anyway how useful such a tool might be?

How well are they holding barstock?

Would they be useful for cross-drilling a bar (where geting rid of clamps can be a great advantage) or maybe for light milling operations, particularly if bar can be axially supported on one end to take a force of cut?

Do you have any experience with these and if so then what is your opinion about them?

 

Edited By Martin Dowing on 24/02/2021 20:30:34

Edited By Martin Dowing on 24/02/2021 20:33:23

Thread: Help with potential first lathe. ML7 content
21/02/2021 00:03:06

Judging lathe and woman only by photo carries comparable risks.

There might be a beauty outside and rot inside.

Regardless of what is being said about hardly ever used lathes etc the truth is that nearly every ML7 currently on the market is going to be a reconstruction project, particularly if it is *precision* what you are looking for.

Dedicated modellers who care about their machines don't like to part with them easy and even if sold it is often done privately in inner circles, not on ebay.

So you should assume that you are buying set of castings with some mechanisms working well and other which don't. Fortunately it can all be rectified to pristine and often better than original condition, very much like I did with my own.

Make sure that you pay attention to detail and material specification while undertaking such project. 2 screws might look identical and yet behave entirely different once fitted.

By doing refurbishment by yourself you will also learn how lathe works and this is always a great asset.

ML7 is easy to understand and averagely intelligent person can work out many things by himself and it is a great fun. Certain aspects which are more specialistic are well explained on the net.

Martin

Thread: Honing tapered bar or bore
19/02/2021 22:42:10

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

19/02/2021 21:46:55

@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.

19/02/2021 20:42:32

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

Thread: ML7 Leadscrews/nuts Still Available?
19/02/2021 17:07:12

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

Thread: What tool to use please
18/02/2021 23:21:52
Posted by SillyOldDuffer on 18/02/2021 21:33:34:

Sam may be guilty of cruelty to machine tools if this job is typical!

Stainless 316 is on my avoid list because it work hardens. That roughly shaped octagon causes difficult interrupted cuts likely to break carbide, which is otherwise a better bet than HSS. 316 conducts heat poorly causing HSS to overheat and blunt quickly. The web recommends flood cooling HSS and 316 and also making sure the HSS stays sharp throughout the cutting. About 60 RPM for 85mm diameter.

Before turning it, I'd round the blank more with an angle grinder and remove the hangers on. Then very light cuts with carbide at about 200 rpm until the circle is formed, at which point go in a bit harder. I'd expect the disc to work harden as the tool rubs either side of the peaks, but carbide should cope without breaking provided it's not asked to chop metal too quickly.

Holding the blank is tricky too: it needs to be rigid with no chance of coming loose. Not sure what to suggest. I would try super-gluing to a fat mandrel as well as bolting. A problem with bolting as shown is shock loads tend to loosen the nut.

Dave

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

Thread: Pulley design
17/02/2021 23:02:28

@oldvelo,

I think, I misunderstood you.

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

Thread: 90deg center holes for grinding between centers
17/02/2021 22:15:16

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?

Thread: Pulley design
17/02/2021 20:57:08

@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

Thread: How Many People Does it Take to Change a Lightbulb on the Forum?
17/02/2021 15:45:34

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.

Thread: Pulley design
17/02/2021 15:03:21

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

17/02/2021 08:24:18

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?

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