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|
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.
|Thread: Indexable tool insert replacements|
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.
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?|
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.
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|
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?|
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?|
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|
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.
|Thread: Honing tapered bar or bore|
Thank's all of you for comments. So after all there are ways to lap tapered parts.
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
|Thread: ML7 Leadscrews/nuts Still Available?|
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.
|Thread: What tool to use please|
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.
|Thread: Pulley design|
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|
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|
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.
|Thread: How Many People Does it Take to Change a Lightbulb on the Forum?|
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|
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.
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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