Member postings for DMR

Its humble pie time. I was not reading my own circuit sketches correctly, which is why I queried it on here, Very glad I did, although my main reason for the post was for the copper versus aluminium windings query, which is not meant as my excuse.

John H, you are of course correct as well; it's an induction job and my circuit was incorrect. I must try harder in my old age.

Thank you Swarf for your input and the previous post. Our sanders are identical apart from the motor fixing and mine is essentially nameless, but I know where it came from. Your motor is on extension pillars to the 3 (of 4) motor fixing bolts, but mine are on 3 separate cast-in frame extensions (See album). There is another apparent difference in that your motor windings look neat! Our connecting wire colours are identical and I can tell you that the white cap is 10Mf and the grey cap is 100Mf. The capacitors are even fixed in the same way, rather awkward to get at the single fixing screw. How on earth did you twig that the white wire from the relay contact went into the motor and came straight out again as a black wire (no internal motor connections) without taking it apart? My rewind will not include that feature! I will retest what is left of my windings again as you have the start winding at 6.6 ohms. Incorrect factor of two on my part as well it seems. I second your observation of the relay ID, I have the same single "up" help marking.

Its going to be a while for me to complete this little job in hand, amongst others, but I will let you all know how it goes. Thank you all for your input.

Dennis

Just ask google for "mosquito+broughton". Lots of stories and news coverage of the crash in Manchester. I lived in a house in Chester until 1984 and it flew over when heading out or back in the right direction. No mistaking those twin Merlins sounds.We always went out to look if we were quick enough as the pilot lived close by and buzzed his own house. Nobody locally would have said that of course if he were still alive. You couldn't fail to love to see it and it never flew at night, so never really disturbed anyone.

Dennis

Edited By DMR on 09/08/2017 21:04:26

Attached picture is for the electrics in a modern disc and belt sander. Associated capacitors say its 2 years old. Relay coil is effectively in series with the start winding and what does that 10 M.Farad capacitor do?
Now then.
The motor is synchronous, rated at 240V 370W and 2850 RPM. It has 24 stator sections and two windings and its cooked. Fault was a short circuit of half the (M) Main windings due to the lead out wire of that winding being pulled tight across the turns.
As an exercise I am looking at rewinding the thing myself. Replacement costs stated as the same as a new complete unit. Damn sure I can make a better job of it than the (ex?) Chinese farmers first attempt. My time is my own and I just fancy spending time doing it. Well I've never do it before! I have part disassembled the remains, determined the number of turns in each segment, assessed winding resistances and generally prepared to have a go at it.
But then I hit a snag. The thing is wired in aluminium and I don’t seem to be able to purchase enamelled Aluminium wire in any gauge in the UK. So I plan for Copper, but Copper isn’t the same and I don’t seem to be able to gauge how I should go about any changes to the SWG, number of turns, etc. I don’t even know the spec for the various aluminium wire grades, although the conductivity doesn’t vary significantly.
1. Aluminium carries about half the capacity of copper.
2. The existing aluminium terminations onto the copper wire tails seem to be steel crimped tubes. another reason to use copper.
3. Aluminium wire has nearly twice the area to give it the same resistance as copper wire.
4. I have been through lots of websites but don’t find anything specific to comparing the two motor windings types. There is a wealth of info on www.electricaltechnology.org. as an example, but nothing specific to what I want.
I need someone with better motor knowledge than I ever had. The aluminium windings approximate to 22SWG for (M) and 24 SWG for (S). I would like to use copper but what would be correct.
Relevant data as found:
M winding 175 metres and 12.8 ohms
S winding 69 metres and 12.8 ohms. Any other required data can be supplied.

As an aside, there is no - what I will call - characteristic smell of burnt electrics in this motor. There was a little puff of white smoke which smelled a bit, but these windings just simply have no smell. Motto appears to be don’t trust your nose any more in modern second hand motors. More pictures in the album.

Seeking someone who knows.

Dennis

Edited By DMR on 09/08/2017 16:35:00

Fake news. The last airworthy Mosquito crashed at an airshow a few years back. It was based at Broughton, flew from there and was serviced there. I seem to recall the remains went back to Broughton. If this story came from someone at Broughton, they deserve the sack for lack of historical knowledge. Come on someone in the know -where is she.

Dennis

Edited By DMR on 09/08/2017 15:30:32

Maurice,

When I said about 'oil holes if necessary' I did not know what you would be buying. As Hooper said, there is no need for any hole drilling in Oilite bushes; they will run for a fair bit of use without any replenishment, provided they are a good fit to start with (and that includes on the shaft). The amount of oil you will use is wholly dependant on your use of the machine and only you can judge that.

As to the original oil nipples, the best plan is probably to just remove them but...............that leaves an upward hole for dirt and swarf to enter, so remove the nipples, fill the resultant hole from an oil can and replace the nipple. Another possibility is to stick a bit of wool, etc in the hole and just keep that moist. I guess they were threaded 2BA so you could substitute nipples for short screws if you want.

As to oil, SAE 30 (a descent motor mower oil, etc) or thinner should be fine. Nothing sticky like chainsaw oil, and never a grease no matter how rattly you find things.

Get going again and see how you get on. It is not a matter of getting oil through the bushes "fast enough" as you imply. Suggest you read up on the Oilite bush to understand better how it is meant to function. if you still find play or any looseness in the two bushes that sit close together, do not try to keep oil flowing through and out of them. It would be futile and a waste of oil. Just put some in (via the nipple hole) from time to time and the bushes will do the job. It is very much a suck it and see, totally dependant on the use the machine gets. There is no need to have oil dribbling out anywhere all the time.

Trust that helps.

Andy,

Its a fairly generic pattern of its day but the colour says its a Chester UK badged machine they called a Cobra Mill from about 10-12 years ago. I've probably got a spec somewhere. The stepper motors are extras and it seems to have a few standard bits missing or detached.

It is MT2 and it will be an all metric machine in its fittings. The height scale says its an all metric machine on its slideways too.

Edited By DMR on 16/07/2017 16:11:35

Maurice,

I have unearthed my early clutch set. It occurs to me that if you have still not shifted that pulley of the shaft end then you cannot reinsert the shaft properly anyway. The pulley on mine is held by two grub screws; do you mean you cannot get them out, or that, having unscrewed them the pulley won't shift (in which case use a hammer but don't break the casting)? If its the former, then you have a problem as they are probably in recessed holes. Which is it? Having removed the grub screws that shaft will knock off.

Dennis

No further responses again Maurice, so......

You seem to have come to the right option to replace the bushes with bushes. Unless you opt for a modern clutch replacement which I can promise will solve your problems. If you can see that the existing bushes have marked the shaft, then new roller bearing are not likely to be a sufficient fit to work at all. You should also consider replacing the bearing in the pulley as it may well have been stressed while the shaft went out the wrong way. As to your original query about getting the old ones out and the new ones in, you seem experienced enough to know that you need to keep things square on to the recesses and use a press if possible, not a hammer!

Plenty of sites for "bronze bushes", take your pick and good luck, but remember to drill and oil hole if necessary and debur before you push them in.

I can send you the relevant pages from the early manual about the clutch/belt replacement if you haven't got them.

Ah, you just beat me to it Maurice with your 17:38 response, but the ball race should not be a loose fit on the pulley if that is what you mean?

Dennis

Edited By DMR on 14/07/2017 17:55:08

Myford would have a reason to say that. Safe to assume that the shaft to the right of the roller bearing in the pulley is slightly larger diameter than the hole in the roller bearing in the pulley and the "hole" in the centre of the needle rollers or bushes in your case. A locating face to tell you when you have pushed it in sufficiently from the tailstock side. So since you have knocked it out the wrong way, you have either:

A) A damaged shaft or a damaged roller bearing or both. Or it has been done before anyway.

B) Since you say the bushes were worn anyway, then you haven't done any more damage to them than is done already. I still have my complete early clutch and covers under the bench, but it would mean me having to strip it down to take accurate measurements for you.

It was the needle rollers that made all the noise. Since you didn't have any, it suggests that the outer bushes on the shaft and the bearing in the clutch were all bouncing around somehow. Did it rattle with the clutch engaged?

Sorry for the negative again, but keep trying.

Dennis.

I seem to recall plain bush replacements as an option to the needle rollers at one time, and someone here may be able to help you if you should go down a bush replacement path. But really anything could have been done to the housing and/or the shaft (less likely as it's tough) to effect a fit. I cannot recommend going down the replacement needle roller path as you will find that it most likely still rattles and spews oil out. There are various questions on here about the problem, if you do the simple search for "Mk1" or "S7". The best answer is to go for a replacement clutch assembly as I did, and others have done. I can talk you through that as to what you need/ don't need. PM me if I can be any help. Another point is that if the shaft has ever been bashed out the wrong way - towards the headstock - at any time then it is messed up anyway. Page 32 in my early manual.

Sorry that it's somewhat negative for what you planned. Keep trying.

Dennis

The S7 Plus nose thread is documented as 42.5mm x 2mm pitch. So from tables you need the female thread depth of 0.54127 x pitch = 1.083mm. Hope that helps.

Dennis

Ken,

Just points.

The early S7 mandrel cone has nothing rubbing on it. I do not feed my Mk1 mandrel from the reservoir via its tap (as Myford called it) continuously, I just dribble some in whenever.....there is no signs of wear on the cone from the year 1954, whereas there is visible marking on the mandrel of the younger wick fed one. I renewed the wick on that when I bought it as the end of it was hard and the large diameter not very long, but you have no way of seeing how worn the wick is without disassembling the machine! And on top of all that, a real Myford engineer years ago admitted that the glazing over of the wick was "a real possibility".

The sole reason Myford changed the design was on production cost issues - just consider the different engineering costs in the examples you have. the later wick is certainly not an "improvement".

A point to your "build from bits" statement. One of the last jobs on a new Myford was (still is if the new lot bother) to align the tailstock height-wise. The base of the tailstock was selected from stock to correct any error and skimmed if necessary. You will be lucky if you line up exactly without some shimming or other adjustment of the base piece. Now if your early headstock is a twin for your tailstock, then no problem.

Dennis

As an owner of both a Mk1 and a Mk2 (as you call them) I would do the reverse to you. The early headstock was far superior to the newer one. Myford changed the design on production cost grounds. If the felt pad you are changing ever dries out, it tends to melt/glaze over and chews the cone bearing. A Mk1 to Mk2 clutch change is a very different story.

Dennis

Is the big bore S7 wick the same as the older/earlier S7 one? I have no idea, but the numbers for the item on their web site are different. Ask new Myford if they have sent you the right, one assuming you got it from them.

To my knowledge there was never a variation in diameter on the earlier S7 and obviously the item should not be a tight fit. The felt you need is on the Myford site as "H68. LUBRICATING WICK A3610/1"

Dennis

Hi Brian,

Short answer - no and no. It is not as you call it a "little outrigger housing". The cog positions are part of the gearbox casing at that end. The 18T is on the top shaft at the opposite end to the modern 26T driver. The idler gear is on an extension to the intermediate shaft which does not come out of the modern box at either end (it's there as a collar only). The guts of the boxes are identical but the casing changed shape. In any case a bigger cog will not fit onto the leadscrew (against the bed) in the relevant position. It's no problem for the 52T at the other end. It's a non-starter, so to speak. No idea how many early boxes still exist and the first one was certainly not QC0002. The aluminium casing covering the cogs was complex and heavy and was always likely to get smashed up by the saddle. Not easy to fabricate/copy. I have given 2-3 people details of it but no-one ever came back to say they had managed to make one.

PM me and I'll send you some pictures if it still intrigues you.

Regards, Dennis

Very impressive. I didn't consider that. You have clearly mastered some arts.

Dennis

Just to fill in some gaps on this thread:

Brian, the early gearboxes before QC2501 had an aluminium cover at the tailstock end with 18T(gearbox output)-30T(idler)-18T(on the leadscrew, also at the tailstock end). Fine feeds were the same.

Simon, as you may have realised by now, you cannot fit a 17T cog on the tumbler assembly as it would cut into the keyway, being too small. The metric set on e-bay as advised by John S is for the later gearbox, but the metric quadrant piece in that picture is the same. The tables appearing on this thread will not work on the early gearbox. If you want further help you can PM me, but I have never worked out the various approximations to metrics for the early box.

Dennis

Search for "Clutch" and you will find lots of previous Myford info. Not a job to be taken on lightly as the long internal spring needs a lot of compressing, but there are ways people have worked out.

As ASF says, the headstock screws mentioned are not adjusting screws! I get the impression that you are short of a a S7 manual? I am only about 15-20 miles from you and have sent you a PM.

Andrew,

I typed "Acme" in the search box and found this quickly:

http://www.kingston-engineering.co.uk/downloads/standard-screw-datasheet.pdf

Bumps you to the top again in case anyone has other suggestions.

Dennis