Member postings for Robin teslar

Hi Myfordians

I daresay this question has already been asked, if so pls link me. I ask if anyone has converted the original BC 1/2hp sp 240 v motor for use on a vfd. Note this has start and run windings controlled by a centrifugal switch (not capacitor start).

Will bearing arcing be a problem provided I screen and earth properly

How do I switch to reverse safely? Stopping first of course

Will this type of motor provide dynamic braking and need a db resistor?

I am not looking for a wide speed range say 20 to 150%

Im floating in the dark here in a pool of techno babble

Robin

Indeed you do need to lock the chuck. But reverse screwing does work and is effective but you have to turn the tool piece upside down. I have done this on production work and it halved the time of conventional screwing because you can go so much faster with confidence, much to my foreman's amazement, but he was a traditionalist

Important use of reverse is for cutting screw threads, as you can do a fast cut with the toool bit moving away from the chuck! and not have to rely on a primitive feed stop

Someone described the ML7 as a hobby machine. Well I thought about this. In some ways larger machines like the Harrison and Colchester are easier to use, but the ML& is always challenging you to find ingenious ways to problem that would be nothing to a larger lathe. But to use an ML7 fully you have to apply a good deal of skill and artistry as well as TLC.

Mine's got the temperament of a Jack Russel

Hobby machine no way hosay

Robin

Ps I've also got a Westbury vertical mill, now there's an even bigger challenge

Well thanx guys, the mists are clearing and I can see a way forward. The whole carbide technology is a bit daunting though.

Indeed the Dewhurst switch is a poor solution for DOL switching and I have a proper MEM push button job, old, battered, works well and has an overload thermal trip. As for the reversing switch, I used a simple 10A toggle switch. As this is only ever used to change winding polarity at standstill, it is perfectly adequate for the job and cost £2.50

But there are purists who will poo poo this

the myford motor is a relatively crude capacitor start type , it has a centrifugal switch inside to disconect the start winding once running, this creates a visible flash each time which to me means contact wear and ultimate early failure. Its just so easy to slip the belt, which becomes quite loose on the pulley

Well I want to see if I can machine HT steel as used in bolts. HSS wouldnt last 2mins. you cant hacksaw the stuff.

Thanx for the tip Dave, I have been chatting with Cutwell and they seem to think ht steel grade ansi 8.8 or similar is no problem. I dont think they do a tool holder with 8mm shank to suit ml7 but i have one of their 20mm ones which has been step mill down to 8mm so I can use a TPMR bit (triangular). The original tc bit is chipped on all sides, seems to be prevalent. Is this a feature or just inexpert use?

I came across this link and its describe as "basics"

http://legacy.secotools.com/upload/north_america/usa/kalamazoostep/Turning.pdf

28 pages of elementary stufff and it stewed my brain already

I remember as an apprentice going to Earls Court for a machinery exhibition and being astonished at the sight of these new fangled ceramic tool bits. taking a large 1/4" bit out of a 2 " billet of steel and travelling at a frightening rate of feed and speed. A long blued tail of swarf flew of the machine. The operator then touch the tool tip to show how cool it and the result was a virtual mirror finish

left me gobsmacked and that was 40 years ago

Yes I expect so, just I didnt come across this obvious trick whilst browsing the dodgy myford clutch subject? Its such an obvious disadvantage for the myford.

Hi ML7s

I read comments on fitting the Myford clutch kit and how it seems to become troublesome. Of course its not advisable to keep switching the motor on/off. It will heat up and also you wear out the internal winding contacts quickly. So what I do is use the lever that tensions the belt and allows you to swap pulleys. It works a treat, so simple

Surely others must have thought of this?

Robin

Hi Myfordians

I daresay this question has already been asked many times before, if so please point me to links. I want to try out using carbide tips for turning but the whole subject is vast (the Kenametal catalog has >750 pages). Ive only ever really used HSS. There are so many different grades and shapes I dont know where to begin. They are not that cheap to make a mistake with.

Can anyone show me the way, its given me a headache

Keep on turning

Robin ML7

Thanx for that link, fascinating who d'a thought it, the cheapo consumed 8 times as much as the mito when switched OFF

So if your caliper is going to ly in a drawer for months then take the batteries out

Indeed the point of my OP. I was amazed at how this cheap caliper could go suddenly wrong and loose its datume without warning. It didnt just wander a little bit, It would go completely wrong. I had to take the best of 3 readings to have some confidence, and move the slide gently. Waste of time.

But you see guys, the old mechanical methods were reliable as much as you respected them.

I hope you understand my point

Well a MEW can't have a "blonde moment", what a silly Billy am I. Will try that soonest. Thanx

Many thanx for the link, I have studied it assiduously. I should have done more homework first and now waiting for delivery of my used digimatic (which seems to have come from a genuine home) will report findings.

BTW I also acquired a battered old Mito dial gauge model 543 180 for a £5 on ebay, absurd resolution 6 sig figs, way overkill on a Myford 1 micron?. It work very well, very smooth and the genuine "old" article

I only wish I could cut down on the digits to say 4. I only have to cough and it moves last digit. Amazing

Yes I've got a mechanical one with a dial gauge as well, nice and reliable

All valid points made here, I just posted my experience to show how these relative calipers can go wrong (not through any abuse or cutting fluid on my part btw)

On the subject of fakes can anyone advise on how to spot a fake Mitotuyo

Hi all, a few years back I was amazed at the availability of these cheap digital vernier calipers <£10. So I bought one and then looked into the amazing technology a bit more. I wont labour the point cos I'm sure most of you MEWs know that there are two types relative and absolute. Well the cheap ones are of course relative. It started out ok then started to misbehave resulting in scrappage. The zero on these sometimes without warning shifted giving false readings. I ended up taking best of 3 zeroing each time - great waste of time. Finally it became completely erratic and I couldn't switch it off. So I am now the proud owner of a Mitutoyo from Ebay 2nd hand for £30. I should have got this in the first place and it is of the absolute type.

So Friends, don't waste your money on these DPRC knock-off copies of the classic Mito

Hi All

I think we may be straying into the realms of esoteric measurements more applicable to aerospace toolrooms than home modellers. My OP highlighted a serious flaw with using the cheapo calipers (called incremental types rather than absolute). FYI the Mitotuyo uses incremental ladder scale together with a reference track that checks with the datum point - clever stuff I dont really quite understand but its termed and absolute vernier and you have to move the jaws a little to reset zero.

It wasnt so much a concern over temperature expansion etc. I observed that my caliper would inexplicably jump to a completely different reading of several mm out from true zero. I found I had to be sure to zero each time and move the jaws slowly. Its a time wasting operation you dont get with mechanical micros and verniers

I wouldnt trust digitals for critical machining measurements. I wonder how people fare with domestic machines using DRO (as opposed to industrial quality machines)