Member postings for Michael Cross 4

My original point was that changing speeds using a VFD is not a panacea and the view that it's a simple substitute for mechanical gearing is too simplistic, which I'm sure you agree with.

Yes Tony I completely agree with you I think our views on this are very close together. I was addressing John.

My point is that:

you don't get the increase in torque that you would from mechanical gearing

Constant torque is one thing, but mechanical gearing increases your toque and adjusting the frequency doesn't, so for a given speed you end up with less torque if you use your VFD to reduce speeds than if you shift the pulleys / gears.

I can't be the only person who has noticed that machines fitted with single phase motors attract a significant premium over three phase machines so obviously not everyone sees or understands the benefits. It's usually cheaper to fit a used three phase machine with an inverter than to source a single phase machine. It's also usually much easier to equip a three phase machine with a VFD than to replace the motor with a single phase one because single phase motors are much bigger for the same power, so if you go that way you're quickly into new mounts, adjusting pulleys and so on.

The benefits of changing speed using a VFD are sometimes exaggerated as if you do this you don't get the increase in torque that you would from mechanical gearing. This is why Variable Speed DC motors (which are actually three phase AC motors) stall so easily when you run them slowly. Any three phase motor will do the same if you turn the frequency down and then push it. Running significantly outside of the designed frequency is also not great for your motor, particularly if this leads to stalling, which robs you of more torque, stalls more easily and the death spiral continues. It's fine as a way of fine tuning your speeds but it's not the ideal way to adjust your speeds across a wide range. That said it is convenient and if you're well within your machine's capability then you might reasonably accept the compromise.

Regional differences in the use of VFDs are more likely down to availability of used machines from industry than this or that place being 'backward'. Here in the UK we are blessed with a plentiful supply of both good used industrial machines and VFDs so putting the two together makes perfect sense. I don't know if that's the case in OZ but that sort of reason will surely explain any disparities.

Thanks again, and when you dress free hand what type of dresser do you use?

Thanks, when you say "away from the direction of the surface of the wheel" does that effectively just mean "down"?

Thanks Clive, if I understand you correctly you're telling me to mount the dresser such that if the wheel were to grab it somehow then it wouldn't be able to cam into the wheel, but rather would be spat out. Is that right?

Should one also dress the wheel by hand sometimes, or only ever with a mounted dresser?

John: I could mount the dresser in a collet or in some other way no problem, it's just that since it came with the machine I imagined it to be usable as is somehow.

I'll look for the quorn book, thanks.

Tony, I suppose I want the ability to dress either of the standard wheel shapes, which is to say a cup wheel and a disc wheel.

Please forgive the basic question but this is my situation:

I recently acquired a Clarkson T&C grinder and am figuring out how to use it. The user is quite helpful with all the grinding, but as far as wheel dressing it simply says "dress the wheel" which rather leaves me wondering what the correct procedure is for this.

Amongst the tooling that came with the machine is a diamond dresser mounted to a stand, which is is about 1" taller then the centres. I think it may have been taken from a different machine. It can be mounted on the table, but only sits fully on the table if the foot of the stand runs along the T-slot, which doesn't look right as this means the dresser is parallel to the axis of the table and wont sweep the wheel with the table in its usual orientation. I can mount it with the dresser perpendicular to the table but that leaves it overhanging, which might be workable but I'm just not sure.

Any guidance anyone can possibly offer on how to go about any aspect of the wheel dressing would be much appreciated.

Thanks

Thanks for the various suggestions, I was really looking for the least possible hassle solution and in the end I found a used one.

Doh! how didn't I spot that? thanks.

Thanks Martin - in an effort to be less vague: I need a UK supplier for a 6" Handwheel with a 5/8 bore and a 3/16 keyway. Are there any other details that would help?

...and to be honest I'd prefer an easy way that I don't have to spend time on.

Boring one wouldn't be a problem but I don't have a way of cutting the keyway.

Does anyone know where I can buy bored and keyed handwheels in imperial sizes?

The only ones I can find online are metric, whilst I could bore one out easily enough I don't have a means of cutting the keyway.

Thanks

Thanks, I've just seen your rebuild; looks great. I might be back for more advice!

Hello,

Can anyone advise on the best way to remove the knee from an Elliott Omnimill - should I leave the knee attached to the screw and lift if out all together or is it possible to detach the screw and lift the knee off (which would me my preferred option)? If so how do you detach the screw?

Also - might anyone be able to help me out with a pdf manual?

Thanks

Thanks KWIL, yes clearly a different variant. Mine's actually a T300 (which comes in loads of variants). It has an M300 head-stock and an M250 gearbox and lead-screw. I'm not sure which the carriage is.

Thanks also old mart but I'm not a fan of linked belts.

That's what I'm thinking as a first option - I don't want to hit that thing at all if it can be helped. I know that roll pins are meant to go in easily but I've also known it not to work out that way from time to time.