Member postings for Ajohnw

The way they are probably made the actual angle doesn't matter as the mating parts can be offset and machined at the same time, in this case it might be by just by using the same tooling.

This is how slideway grinders tend to work on prismatic beds. The saddle is carried on a sub table and offset so that grinding one side of the V on the bed grinds the opposite side of the V on the mating part. It helps insure that the angles actually match - the important aspect.

John

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The problem though is that the same is true of brushed motors. How some one might go about that can vary from simple as per electric drills etc and it seems electric model loco's or in more complicated fashions.

Actually they tend to be constant speed devices as the back emf aspect is self correcting, motor speed goes down, back emf drops, current goes up stable speed achieved again - if only it was really as simple as that. With super conductors it might be. There are also the various types shunt, series and a mix / compound motors. There is a noddy view on these here

**LINK**

A brushless or perm mag motor has to effectively be shunt

John

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If the pivot point of the larger wheel is fixed and adjustable that could do the sort of thing you seem to want. As drawn there isn't anything actually determining what the larger wheel rotates about so it might do any old thing.

Say you have a T slot running across the larger diameter and use that to locate the position of the pivot the larger wheel is going to spin round on. That locates the point it will revolve around. Your slot wont.

John

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Actually Neil by looking at the voltage and current behaviour of a dc motor it is possible to maintain a constant speed with varying load but the usual way is to fit a tacho as it's more precise.

Also the basis of vector control of stems from this aspect and it's eventual use on 3phase ac motors

**LINK**

Forgot add that the same principle has been used in electric hand drills and related items for a long long time - even electric model loco's.

It sounds far more impressive when some one comes up with a nice technical name for it.

John

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Edited By Ajohnw on 11/02/2016 13:25:27

Wrong Neil. They are driven is a loosely similar fashion to stepping motors. In practice they are perm mag motors where the com has been replaced with electronics. In fact in theory some one could take a perm mag motor and convert it to brushless but they would have to take the drive off the case, a so called out runner.

When they could be found servo motors for some application could be driven from rectified mains. Due to them being so over built for reliable long term operation.

John

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There seems to be a manshed building up in B'ham. Not sure what they have or do but they have placed an add in homeworkshop to dispose of a few things.

A mans shed seems to be the equivalent of a club where things are actually made now.

John

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The level of field excitation plays a huge part in how dc motors behave - including allowing hill hold in the case I mentioned. LOL Downhill hold has more limitations but vehicles generally have brakes but in other case the regen can be varied.

AC inverter drive are constant torque from zero speed with a catch that we all know about however there are various type of inverter rated motors.

John

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It's nice to be able to get ctrl right to bring up the spell checker - I left toolbar as one word and think it should be now.

John

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The EV's I worked on Andrew did the same with a DC motor.3 tonne GVW, van, single decker bus / coach and a taxi. They all did a real 50mph under normal road conditions not just on the flat, no clutch no gearbox and not a lot of gearing down to the drive either.

Some were also working on ac drives but it was a tough / inefficient method using the semiconductors that were available in the mid 70's so never went anywhere. I'd be more inclined to say impossible really at these power levels with any sensible levels of efficiency. Transistors 1/2 the size of a house brick also had problems competing with thyristors in a number of respects.

The bloke that initially developed the motor could actually pick it up and carry it around - No one else I know could and I expect he used it as a form of weight training.

The starting torque problems of AC motors that I am aware of mostly relate to single phase drive. Hence machine tools mostly using 3.

And as to brushless I can't really see them competing with what sep x can do if needed as the field on them is fixed.

Some of the claims for all sorts of things are crazy. I can remember reading about room temperature super conductors in Nature donkeys years ago. I just can't understand why they haven't hit the market.

mmmm I just wondered what would happen if the magnets were moved further out mechanically.

John

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Edited By Ajohnw on 10/02/2016 23:37:47

Edited By Ajohnw on 10/02/2016 23:39:17

All BL is Neil is a dc motor that replaces the com with electronics. It's as simple as that.

John

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Interesting. I have just found that if I ctrl right click I can use my spell checker. This only happens if it's an underlined error. It worked once anyway.

If I right click on a line that contains text I just get paste.

For copy paste I just use the browser facility rather than the one the forum uses. One irritating aspect of that is the font size may change but only going smaller. I tried larger out of curiosity. I notice that the font size on this forum is smaller than any other ones I am aware of. I've never been entirely happy with that aspect. I use a large high res screen. That might or might not have something to do with it. I suspect this must be tough for people who have significant vision problems.

John

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Edited By Ajohnw on 10/02/2016 18:02:15

Shift F5 cured it for me. It happened recently. Might be down to the site being mentioned on here.

John

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The characteristics of a dc motor are down to a back emf being generated. At some speed this balances out the load on the motor and it's internal resistance. If the motor speed is forced to drop due to load the back emf drops as well causing more current to be drawn, speed to increase and the back emf to balance out again. There are various aspects that prevent this from being perfect but it's why dc motors some times get burnt out. Controllers too. It makes electronic control less reliable unless motor current is sensed or the set up fused well enough - that aspect is not at all easy when electronic switching is being protected. The easiest answer as far as the electronics are concerned is to use well under rated components. That way quickish blow fuses can be used for protection. It's pretty easy as far as the motor is concerned but in both cases will get a bit complicated because the time the conditions exist matter as well. Some period of overload will be ok - or should be in practice.

There are more variations. Permanent magnet being one plus series wound, shunt wound and a mix of the two.

Where there is a field winding the best form of electronic speed control involves switch mode driving the armature and the field separately. Usually called sep x. It can offer a much better usable speed range. The same would apply to a brushless motor of the same basic type.

John

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How did you get on with the headstock bearings Alan. I've always wondered if they can be changed cheaply.

The reason I ask goes back to training. The chipmaster was the only lathe that around 20 people a year used for a bit short of a week. It was one of the few lathes that turned rings due to slight bearing wear. This gives a pretty good finish with the rings every now and again along the length. It was the only lathe we were allowed to use emery cloth on. Some others had the same sort of problem but usually depth of cut could be used to up the load and get rid of the play - !##!!??? they made us hand feed for a long time on those but it does come with practice. Slightest change in feed rate produces a ring,

Intsructors mic'd up all of the work and checked the finish and then stuck a pin in a board - colours ranging from black to gold. Gold helped the tool bonus a lot. Black not at all, might even reduce it.

The work done on it was all smallish, max 1/2 dia or so and this one was used because 3000 rpm speeded up the work rate. Some one did look at the bearings but reckoned that they weren't adjustable - I just fetched some emery cloth out of the stores. The rest of the lathe was perfect.

John

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Some one mentioned a company that will buy or sell loco's on commission who reckoned that they were fair. That may be a more sensible method than a private sale. Not my field but given the prices of completed ones and even castings these days they can be worth a lot of money.

It's usually possible to get some idea of the value of equipment by searching for it on ebay and also by using the completed listing option. That will show items that have actually sold. Lots of equipment is sold on homeworkshop.org. Model Engineer seems to vary, some items go quickly. My impression is that some dealers use it. They also use all of the other usual places to advertise as well. Some people have bought the wrong thing and expect near new prices too. Many people expect a decent saving even if the equipment has hardly been used. I also think about what I would get for it if at some point I wanted to sell it. I mostly buy used equipment sometimes just to try it out and if not what I want sell it again.

There are also several companies around that mostly sell used items to private buyers. One thing I think is missing on this site is a page of links but I can understand why they use companies that pay for advertising. Some model engineering clubs around the country may have links but of late for instance the one local to me in B'ham has none at all. It did have lots of useful ones.

One thing I have noticed, to my own benefit actually is that when something like a fully kitted out lathe is sold on ebay people may bid a bit more than the usual prices for the lathe but not enough really to cover what is being sold. My current lathe was bought like this. The seller listed it with bids and a reserve price. I was the only person that placed a bid over the reserve price. The others were well short. He would have done better if he had just stated a price as I would have paid more. If I had thought that price was too much I would have contacted him to negotiate.

Dealers will buy private sales if the price is right. They generally have to be more expensive than private sellers due to VAT and the fact that the equipment may hang around for a long time. When they are offered items to buy the prices they offer are usually extremely low. Some of my equipment came of some one who had tried that. At the time the local Bargain Pages was a good place to advertise. He did and sold the items for similar prices to what the dealer offered him - these were way too low really but the dealer had annoyed him. The dealers mark up would have been amazingly high on some items because they might take a long time to sell. Couple of hundred % at least on some.

John

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I'm guessing it's a height or maybe cross wise alignment error Jason as well. The way it's put together is a tough call. Can't be sure but it looks like they are mounted on wood. If the parts are spot on a small brass plate would give more certain results and if the parts were made from scratch would also help bore them along with getting good alignment fairly easily.

John

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You could try loosening the screws on each of the bearing supports in turn allowing one to move if needed. Any axial miss alignment between the bearing housings will stiffen up the bearings.

One way to check further would be to remove the housings, put them together and fit the axle. If you run you finger tip across the bases it's possible to feel errors of a few microns.

The base not being flat could cause similar problems.

If this is causing the problem the looser fitting axle may be better providing the error isn't too great.

Reading your last post Brian I would suggest trying to get some idea of how much error you are dealing with. A simple paper shim might fix it. Maybe even aluminium foil.

John

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Edited By Ajohnw on 10/02/2016 10:08:21

It's not unusual to see items on ebay selling for more than the new price on things like steadies. Also items that turn up in an Amazon box. Think you can guess why. I bought something once without checking around new and about twice the price of what Maplin sell it for. No one would look for stainless steel weighing scales there.

I talked to some one who had bought a number of harrisons a few months ago. He reckoned that they were made in Taiwan and just assembled in the UK. He initially thought he was buying UK product.

Taiwan was the place the cheap lathes came from. They are the people who thought ahhh why use hardened bearings on hobby machines. Maybe hardened ones are used now. India has a brief spell too at one time. It seems that their Myford clones were very good.

John

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Cushion flooring is a type of lino that has a spongy sort of feeling to it. I haven't had problems with treading on swarf which might then cuts into it. It was down when I set my stuff up there. It was down when we moved in about 28 years ago. Given what the previous owner did for a living it's probably the highest quality stuff.

I replaced it in the kitchen which is adjacent around 15 years ago. Still ok apart from our dog leaping about and her claws taking off some of the surface covering - leaving grey marks. She's a very lively german shepherd who even at 9 still thinks she is a pup. This is probably a cheaper variety. I had it fitted very quickly as a surprise for my wife.

If only I can get a builder to do something with a wall and build a new one my workshop will be similar to Steven's shown earlier. If we move out it will become a utility room. When that is done and the kitchen re jigged I may install the washing machine under the lathe - a bit of sensible give and take. My wife would be happy with it being in the kitchen where it currently is but she loves to fill all available cupboard space.

John

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Actually most of my attitude to them is in comparison with a conventional counter shaft lathe where it is easy to change speeds with a belt even on my me10 boxford which is a bit of a pain in that area. Myfords are a lot easier.

I wouldn't be totally happy with a lathe were I had to swing the cover off the end a play with difficult belt settings but have - hobbymat, unimat, chinese. Compared with that yes variable speed is great with some provisos. Jason mentioned one, diameter speed and cut depth. Brian mentioned another case of this on his baby lathe turning cast iron. He doesn't want to try that again I say basically fine but do appreciate the limitations. They are more important at some lathe sizes than others. Providing the power levels needed are improving.

Variable speed conversions are a touchy subject. There are people about who will post a video showing a short sharp hefty piece of work being done with an ac motor being run at a very low speed/ Isn't it great etc. It can be done if the motor that was fitted is powerful enough and many are when over loaded but if the motor is run like that often without sufficient longer stops to allow it cool or run like this for longer periods it will let the smoke out. I haven't seen any claims like these on here, only the opposite. Good because the other way misleads people. Actually there is a better solution to this problem that people don't seem to use. I'm sure my Boxford would run at heavy loads a bit short of the motor ratings for weeks over a 2:1 speed range without changing a belt setting.

I'm toying with the idea of going back to pure belt - even with sophisticated switching they are a lot more noisy.

I've heard that the larger VS lathes fitted with ac motors are also fitted with a separate cooling fan. I'll be interested so see how that works out. I am going to try it on something that doesn't matter too much at some point. Not my lathe though.

Reliability on the vs lathes does seem to have been a bit mixed. Pass on that. Lots use them and only a few complain. My impression is that it could be more of a mini lathe problem. I didn't have any problems with a small VS mill I had that used the USA controller design but the noise from the low speed gear irritated my wife. I would much rather have had a belt and more than two ranges but it did what I and the subsequent owner wanted.

John

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