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What to drive a J & S with ?

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Chris Crew19/09/2021 13:25:16
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134 forum posts

Gerry, with the greatest of respect, don't you think that you are massively over-thinking all of this? For heavens sake, over 20 years ago I plugged a J&S 540 into a Transwave 5HP static converter with no thought other than getting it to run and it has performed superbly well ever since. For the purposes of a back-shed workshop, which I am assuming you have like most of us, the surface finish on my work has been very good and the machine or power supply have never 'wobbled'. I accept static converters, or even maybe also rotary converters, are now yesterday's technology but all the same they provided the power we needed at an acceptable price and convenience when nothing else was available.

I apologise for these comments if you are NPL trained and want to achieve near-perfection but for all practical back-shed amateur purposes you really don't need to go this deeply into things, just plug the machine into to a suitable power supply and see what happens. I can almost guarantee you won't be disappointed if your J&S is in a reasonable condition. You can make all the adjustments and refinements you may think, or find, are necessary later and most will be in the type of wheel that is fitted to the machine.  You may have to change it for a different grit and bond but the chances are your machine will have been fitted with a good general purpose wheel which will cover the majority of your requirements and expectations of finish.

Edited By Chris Crew on 19/09/2021 13:37:45

Andrew Johnston19/09/2021 13:38:18
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6264 forum posts
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A) As per Dave, select the drive according to the input VA. In star each phase winding is connected from a phase to a star point. The star point is nominally equivalent to the neutral but is not connected externally. In delta there is no star point, windings are connected phase to phase.

B) Select the drive accoriding to the next size up from VA of both motors.

C) When I looked recently I couldn't find any 1-phase 240VAC in to 3-phgase 415VAC VFDs offered by the industrial manufacturers. There are some "digital" drives advertised as 240V in, 415V out, but it's not clear what they are. There's no industrial demand for such a unit. If you get 240v in and out and run the motor in star then the torque will be down to about 60%. If the motor can be connected in delta then the phase currents will be the same as for 415V/star, so the torque will stay the same.

D) It does matter. At no load the power factor of an induction motor is appalling, around 0.15-0.20, so significant phase currents will flow even though the real power is low.

Andrew

Chris Crew19/09/2021 13:56:45
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134 forum posts

Andrew, again with respect, who gives a 'monkey's' about the power factor in a back shed workshop? I certainly don't and I suspect not many other amateurs do either. If you are working in industry and power correction is necessary to achieve maximum efficiency it is obviously very important. When you have finished a job in the shed the machine is almost always stopped immediately so whatever the poor power factor characteristics of an induction motor are under no load become irrelevant anyway.

I know there are some highly trained and knowledgeable engineers on this site, you may be one of them, but applying professional industrial expertise, standards and theory to back-shed workshops is both impracticable and pointless, IMO.

Buffer19/09/2021 15:35:14
293 forum posts
131 photos

I am running a surface grinder with a transwave rotary converter. I am delighted with the finish I get on my loco parts. I have had no problems with it at all and I can switch on or off motors in any order. It is noisy but at least I dont forget to turn it off! It's about as big as a microwave oven but very heavy. I dont have it all wired into sockets around the wall I just have a long lead so i can plug in a tool grinder and a sharpedge grinder as and when needed and then just coil it up when finished. The only down side was the cost but hopefully that's me sorted now for good.

not done it yet19/09/2021 18:50:01
6322 forum posts
20 photos

Running costs may well become more important as time-of-use tariffs become the norm. My day-time leccy cost has risen by about 60% recently. At least a VFD uses naff-all when the drive is turned off.

Andrew Johnston19/09/2021 20:39:43
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Posted by Chris Crew on 19/09/2021 13:56:45:

....again with respect.....

Which is nothing to do with respect, but simply a lead in to egregious nonsense. Had Chris had the wit to read my profile before posting it would have answered his question about engineering. We're left with the thought that amateur has several meanings, but amatuerish only has one meaning.

I am a professional engineer, but largely self-taught as a machinist. That doesn't stop me wanting to learn and try new things, and at least aspire to professional standards. If Chris is happy stuck in his back shed that's up to him, but it's not for me.

As is often the case the comment on power factor completely missed the point. The question was about which motor to turn on first. I think that the OP made an assumption that the spindle motor would be taking less current than the pump motor as it starts off load. However, since the power factor of an induction motor off load is poor the spindle motor phase currents may be higher than expected, and possibly more than the pump motor at full load. The VFD controls current, so that's the important parameter.

Andrew

Chris Crew19/09/2021 21:29:29
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134 forum posts

Well, we will have to leave it to others to decide who is talking 'egregious nonsense' in the context of operating in a back-shed atelier, won't we, Andrew?

Pete.19/09/2021 23:05:47
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638 forum posts
102 photos

I have to agree with Andrew, not necessarily on this one issue, but in general, a home workshop shouldn't be synonymous with people who aren't that bothered about standards.

Forgive me if I'm mistaken Chris, in various threads you've said you own Colchester Student, a Bantam, a Myford ML7, a Myford speed 10, a Qualters and Smith saw, a Jones and Shipman surface grinder, I can't remember what mill you said you had or if you've said you own a drill, all this kit is more like a small industrial business than a small shed workshop.

I am envious you have the space for all this in your back shed.

Chris Crew20/09/2021 01:35:34
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134 forum posts

Pete, I have never once said that I don't worry about standards, or shall we say the standard of my work which is always done to the very best of my ability and scrapped if I am not entirely satisfied. I would like to think that, if not 'exhibition' standard it at least looks pretty good and not at all 'amateurish'. In theory, it is possible to work down to 0.0001" on the J&S 540 or 0.0002" on the J&S 1310 but if I was to work to these limits they would only hold for the time they were produced because I do not work in a temperature controlled environment, so both the work and micrometer would probably measure different dimensions depending on the time the measurement was taken. That is partly why tolerances exist and are quoted on drawings, or were when I was an apprentice but that's well over fifty-years ago now. I have no idea what happens in industry these days with the advent of CAD/CAM because I have never dealt with it. So to me, if it looks right, fits right and works right, then it is right.

The point I was really trying to make, and admittedly this is an assumption, is that we are all practical men and only need our machines to run reliably when we switch them on, we are not in the workshop to redesign them or their power supplies, but we may suggest improvements from time to time. All the clever stuff, the design, the engineering and manufacture has been done by the professionals and is encompassed in the machine when we purchase it. We have paid for the professional engineer's skill and merely use the tools he has produced for our own purposes, including the converters and inverters. Again, I must admit it has never once crossed my mind to fit power factor correction capacitors to the distribution board in my workshop for motors running under no-load or that any phase in-accuracy would effect the finish on my work because for all practical purposes it hardly matters, IMO.

Yes, I am very lucky to have a number of machines that were once found in light industrial or educational establishments but this is because, when Mrs.Thatcher was busy closing down a great deal of traditional British industry and the educational curriculum was changing, they could hardly give the stuff away. Working nights in various parts of the country gave me the opportunity during the day to visit factory liquidation sales. I have seen auctioneers almost crying at the prices they were having to knock down. For example, I once bought a fully equipped Brown & Sharp No.13 universal grinder for fifty quid and it cost me £250 to have it shipped home! I still have the thousands of pounds worth of Burnerd collet chucks and Crawford collets that came with it but sold it on when I acquired the J&S.

I don't pretend to be anything more than a back-shed amateur, but I have every respect for the professional engineer's knowledge and technical education and I am very envious of it because we didn't even get the chance to go to university in my day, although I hardly think that a lot of it is relevant to the practical 'common-sense' issues we deal with in our home workshops and hobby projects.

Pete.20/09/2021 03:23:38
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638 forum posts
102 photos

Chris, the problem with saying it's just a back shed workshop so it doesn't matter is interpretation, generally speaking. To me a back shed workshop is a small shed with a bench top lathe like a Myford, a bench grinder and maybe a small bench drill, a workshop with industrial surface grinding equipment would never enter my imagination in the description back shed workshop.

Yes you are lucky to have picked up all those great machines for peanuts, when I started secondary school in the mid 90's all that machinery was gone, we didn't even get the opportunity to see it let alone get taught how to use it,now all you wealthy pensioners make us younger hobbyists pay through the nose for this old industrial equipment you paid peanuts for, that we didn't have the privilege of using at school because it was gone, so when it comes to maintenance on this old equipment, it is somewhat irksome when I hear the attitude that maintaining it properly doesn't matter as it's in a shed.

Chris Crew20/09/2021 10:46:01
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134 forum posts

Pete, please don't be troubled by the idea that my kit is not well maintained and cherished, although a little under-used these days, I must admit. Just as a classic car or bike enthusiast collects and cherishes the products of the past or the stamp and dinky toy collector maintains his collection just for the sheer joy and satisfaction of owning it, so it is with my machines. In fact, collecting them became almost a hobby in itself because to me there is something rather special about an old British machine tool. They are redolent of the time when this country led the world in their production with some of the biggest names like Alfred Herbert, when men in brown overalls cycled to the works every morning from a terraced house and thought nothing of the wonderful amount of skill and craftsmanship they held in their hands.That may be just a nostalgic fantasy, but just as with a classic car or bike, is it the smell, the feel or the period design that makes them so special? I don't know and I can't say, it sort of just is! What I do know is that the time is fast approaching when I will have to dispose of the collection and downsize the house because health and age issues will compel that to happen and it will break my heart to see it dispersed after all these years.

Edited By Chris Crew on 20/09/2021 10:49:30

Mike Poole20/09/2021 14:41:48
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3071 forum posts
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I distinctly remember being told to start the wheel before turning on the coolant and turn the coolant off before stopping the wheel. The reason was that if the coolant was left running on a stationary wheel is could load the wheel with coolant and create an imbalance that could burst the stone or damage the spindle. If the pump is just for the hydraulics then that will not be an issue.

Mike

gerry madden20/09/2021 21:23:28
201 forum posts
97 photos

Gentlemen, thanks again for your advice which i can assure you was all carefully considered, perhaps too carefully but there you go

This morning I had a very interesting discussion with someone who I was certain would try to sell me something and had he done so I might well have bought it. But after assessing the machine and its motors he actually said he could not recommend his products and that fiddling with the motors was not a sensible option either. In fact he directed me to a company I had previously spoken to. I'm still taken aback by his candidness. Its not often you get this these days.

So rotary converter it is. As Buffer so succinctly put it "The only downside was the cost but now I'm set up for life"

Gerry

Pete.21/09/2021 00:20:17
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638 forum posts
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There's nothing wrong with that Chris, an underused but cherished machine is better than being abused, like the biggest used machines dealer on ebay, home and workshop machinery who store their machines outside under a tarp getting rusty, I cringe every time I see it.

I just don't like seeing things I value highly being treated like junk, I'm glad I misunderstood you.

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