Author Topic: Mini Lathe Speed Reduction....... (Read 33995 times)

Stilldrillin · « **on:** January 10, 2012, 03:36:57 PM »

Early on, last year. I replaced the motor and pc board on my Real Bull mini lathe........ http://madmodder.net/index.php?topic=4962.0

As it was all done in a bit of a rush at the time. I now intend to finish the job, properly.
Including reducing the belt ratio, as posted by Loply, around ½ way down the page....... http://madmodder.net/index.php?topic=4946.0

This motor/ board set up is a lot more lively than the old one. Giving less torque, and 1,287/ 2,920 rpm, instead of the promised 1,100/ 2,500.
So, first I need to slow it down to spec'.

This is my board. MAX, MIN, IR, CL .......

Also, ACCEL.........

Do I switch on, and reduce revs to 1100, using the MAX pot?

I've heard mention of higher torque, through twiddling........

What can I achieve, and how, with the other pots?

Or, should I leave well alone??

David D

John Rudd · « **Reply #1 on:** January 10, 2012, 04:41:04 PM »

David,

If in doubt dont do it...As my dad would say....

Can you afford to lose another board?

I'd say that to gain more torque at lower speed, you need to do it mechanically(keep the motor running high and reduce the speed thru a cog box)...The current setup isnt capable of more torque at lower speed..besides running the motor at lower speeds for more torque will cause the motor to overheat (poor cooling....)

andyf · « **Reply #2 on:** January 10, 2012, 05:28:51 PM »

David,

When all else fails, read the instructions... I think you know where to find them. You should be able to rein back the speed with the MAX trimpot, though it does look as though it interacts a bit with the MIN, so a bit of toing and froing might be needed.

I'd hazard a guess that the IL trimpot might raise the limit of the current which the board supplies to the motor, thereby increasing the torque. Instructions on p19 of the online manual. But get a second opinion from Dave BC or someone else who knows what he is talking about before you twiddle.

Looking back at your "It doesn't work any more!" thread, I see that it concluded with the news that Dave had repaired your old board, so I suppose the last resort is to put it back in, unless he is holding it to ransom.

Andy

Troutsqueezer · « **Reply #3 on:** January 11, 2012, 01:18:49 AM »

Speaking as an EE (my day job) I would recommend leaving well enough alone unless you have a thorough understanding of the safe operating areas (how they are biased and where along the load line they are operating) of all components involved and maybe an understanding of phase angles...well, you get the point. There is much to consider when making adjustments to circuitry of this nature, things that unless you designed the circuit, you have no way of knowing. Maybe you can tweak the pots and everything will be ok, and...maybe not.

Stilldrillin · « **Reply #4 on:** January 11, 2012, 02:15:11 AM »

John, Andy, Dennis.
Thanks for your comments, and cautions, which I have taken on board......

Andy, the only online instruction manual I can find is this one.... http://www.kbelectronics.com/manuals/kbic_manual.pdf Section 7 deals with twiddling.

Is this the manual you are referring to?

The old, repaired board, is still residing with Dave. We'll meet up, sometime. No ransom has been mentioned, as yet!

David D

andyf · « **Reply #5 on:** January 11, 2012, 04:23:32 AM »

That's the one, David.

Andy

Lew_Merrick_PE · « **Reply #6 on:** January 11, 2012, 12:08:24 PM »

This pending project is relatively far down the priorities list, but I will be moving the motor on my MiniLathe out from under the base casting so it can have multiple pulley ratios going into a (to be added) jackshaft that will sit in the (to be vacated) volume. The advantage of this (from my knothole) is that I can get better torque at lower speed ratios and free up the area occluded by the motor cover today (which I will need for my taper turning attachment). My plan at this point (and subject to change without notice) is to mount the motor on a 2- or 3-position lateral slide that mounts to a (belt-tension-wise) second slide that will use a cam to maintain belt tension. That way I can loosen the cam, move the motor to the proper belt alignment position, and re-tighten the belt (fairly) quickly. There will need to be some tin-bashing to make a cover that keeps the swarf out of the drive, but a pivot/hinge and pivot-hook snap latch should take care of that...

loply · « **Reply #7 on:** January 11, 2012, 01:00:59 PM »

Quote from: Lew_Merrick_PE on January 11, 2012, 12:08:24 PM

This pending project is relatively far down the priorities list, but I will be moving the motor on my MiniLathe out from under the base casting so it can have multiple pulley ratios going into a (to be added) jackshaft that will sit in the (to be vacated) volume. The advantage of this (from my knothole) is that I can get better torque at lower speed ratios and free up the area occluded by the motor cover today (which I will need for my taper turning attachment). My plan at this point (and subject to change without notice) is to mount the motor on a 2- or 3-position lateral slide that mounts to a (belt-tension-wise) second slide that will use a cam to maintain belt tension. That way I can loosen the cam, move the motor to the proper belt alignment position, and re-tighten the belt (fairly) quickly. There will need to be some tin-bashing to make a cover that keeps the swarf out of the drive, but a pivot/hinge and pivot-hook snap latch should take care of that...

Lew, not only can moving the motor accomplish this, but here's an experiment for you to try.

Take off the head of the lathe and remove the motor. Observe that the head is bolted to a piece of the lathe bed which is supported at the front of the lathe, but that the corner of the bed furthest from the operator at the left end of the lathe is just floating with nothing supporting it. Pop a dial indicator stand on the bed and put the needle in this corner and push down with your thumb.

It will deflect by a very surprising amount. 10/15mm thick floating cast iron sheet is not very rigid when it's not supported at all.

Moving the motor will allow you to put a "support" in there and will stop the entire flippin' head from rocking and rolling when under pressure.

Stilldrillin · « **Reply #8 on:** January 25, 2012, 12:25:51 PM »

I had a gentle tweak at the control board, the other day.

A very small movement on MAX, reduced the revs to "correct". But, this then caused very slight creep when control pot was turned to zero.
A slight movement on MIN solved the creep, but the top revs increased slightly.

As I often use a 5" chuck, I turned the ACCEL to give 3secs acceleration time. This then disturbed the other two settings..... Again!

Finally, (after 5 mins), all was balanced satisfactorily.

Today, I made the two motor mounting washers, to work with the cradle. Hopefully this will give a more rigid motor location.

Also, I started on turning the pulleys to fit.......

After the speed/ acceleration alterations, the lathe performed perfectly.

David D

andyf · « **Reply #9 on:** January 25, 2012, 02:29:43 PM »

Hi David,

Glad the tweaks to the pots have got the speed to behave properly.

There's a plan of a jackshaft speed reducer here, though it is single speed:
http://www.toolsandmods.com/library/ralph_patterson_speed_reducer_2.pdf

I think you are in the Yahoo 7x12 minilathe group; at least, a couple of messages from a Stilldrillin (but with a surname which doesn't begin with D) recently popped up for moderation, because you/he's a new member. In the Photos section, there's an album called "Belt Drive" showing a multi-speed reducer, though it seems to involve two jackshafts.

Andy

Stilldrillin · « **Reply #10 on:** January 25, 2012, 04:07:31 PM »

Hi Andy. Thank you!

Those two seem very purposeful. Though I wonder just how much torque the gearing can stand.

Yes that is me, on 7 x 12. Still rather smockravelled with the email only format. Not quite as homely as on here.......

David D

andyf · « **Reply #11 on:** January 25, 2012, 07:27:26 PM »

Quote from: Stilldrillin on January 25, 2012, 04:07:31 PM

Hi Andy. Thank you!

Those two seem very purposeful. Though I wonder just how much torque the gearing can stand.
Yes that is me, on 7 x 12. Still rather smockravelled with the email only format. Not quite as homely as on here.......
David D

As to the gearing, not a huge amount of torque, I imagine. From reports on the 7x12 group, the plastic gears within the headstock seem to be those which most frequently lose a tooth. And the headstock end of the bed is cut away to accommodate the motor so much that it might flex a bit with supertorque, as Fergus said. See two of the pictures on this page, which show the Real Bull variety, but Siegs are the same. http://www.toolsandmods.com/mini-lathe-bed.html

Yes, the 7x12 Group is a bit clunky, like all Yahoo groups. Threads on it aren't neatly arranged, as they are here. The format dates from years back. You can post via email, but it's easier to do it by visiting the group. It started as a spinoff from the 7x10 group when that degenerated into political ranting, so is fairly tightly moderated by John "Gadgetbuilder", Trevor Rymell and me to make sure it doesn't go the same way.

Don't really know why I'm a mod, having never owned a Seig or RB lathe.

Andy

Stilldrillin · « **Reply #12 on:** January 26, 2012, 08:04:47 AM »

Quote from: andyf on January 25, 2012, 07:27:26 PM

And the headstock end of the bed is cut away to accommodate the motor so much that it might flex a bit with supertorque, as Fergus said. See two of the pictures on this page, which show the Real Bull variety, but Siegs are the same.

Andy

Andy.
Where's this cutaway?

This is my Real Bull, during a stripdown, some time ago........

Same thickness of bed, all the way through. Full, four bolt fixing.

David D

andyf · « **Reply #13 on:** January 26, 2012, 08:49:07 AM »

Sorry, David; I omitted the link from my last post, but have now rectified that. "Cut away" was not the best way of putting it, but I was referring to how the rear vertical side of the bed stops short and doesn't afford any reinforcement to the top of the bed under one side of the headstock - see the last pic on that page.

Andy

John Swift · « **Reply #14 on:** January 26, 2012, 08:51:57 AM »

Hi Dave

I guess this picture shows the cutaway

without it ,you need extra metalwork to attach the motor

(not what the exra bean counters want when the are keeping the cost down )

John

PS the motor mounting in the Ralf Patterson speed reducer has given me ideas

Stilldrillin · « **Reply #15 on:** January 26, 2012, 10:40:00 AM »

Andy, John. Thank you!

I realise there's a little less metal, in a Sieg version.......

I wondered if the deck was cut away, under the headstock. Or summat!

David D

Bluechip · « **Reply #16 on:** January 26, 2012, 11:01:43 AM »

Hi Dave

I KNEW you'd fix the speed wotsit ..

I had every confidence..

What happened to the squeak BTW ??

Or are you looking for a pip to go with it ??

~~After last nights curry I've got some bubbles if you want some~~ ...

I'm off .... not before time etc etc

BC

Stilldrillin · « **Reply #17 on:** January 27, 2012, 08:03:25 AM »

Hi Dave.
Thanks for your confidence, in my confidence.

Squeak's still there, as it has been since new. No sign of Wilfred, or Pip......

Will post the build/ mods, as they happen. Don't hold yer breath. I'm hoping I can grab a whole hour in there this aft......

David D

Stilldrillin · « **Reply #18 on:** January 27, 2012, 12:54:06 PM »

Dave BC.
I was fiddling with the new pulleys, this aft. Realised I could do a vid, or two......

But, I couldn't make it squeak on camera, for you!

But, here's a vid of the quiet end.........

[ Invalid YouTube link ]

The other end isn't as exciting, but it's a lot noisier......

[ Invalid YouTube link ]

I still think the commutator needs a gentle skim.......

David D

Bluechip · « **Reply #19 on:** January 27, 2012, 01:34:45 PM »

Dunno Dave, does sound a bit ratchetty ...but ....

If I turn the one on my WM16 mill right down it cogs ... and I expect it to really.

With these controllers you are only putting a bit of a pulse through the motor 100 times a second.
So the motor is going to give a lot of little kicks rather than a continous s-m-o-o-t-h rotation.

On my mill it rattles the gears horribly, but if I put some drag on the spindle, it don't, 'cos I have taken the backlash out of it.

I wonder what that motor would sound like using my Variac with a bridge rectifier ???

When the controller went dud on the WM16 I ran using the variac/rectifier for months 'cos I was too idle to fix the Controller Board and it ran a whole lot better. And faster ...

the motor was getting a fair bit more than it's usual 180V ration ...

It may be that the commutator is a bit gruesome. but I would not have thought so, the motor ain't all that old is it?

No harm in having a shufti, make sure the brushes are free too, they can give all sorts of aggro ...
BTW what's all that black stuff? Belt crud??

I'll wind your spare board up with the Warco motor and see what that's like ...

IIRC it doesn't make too much noise.

Hmmmmm hard to tell at this distance ...

BC

Stilldrillin · « **Reply #20 on:** January 27, 2012, 02:05:24 PM »

Over seven years of belt crud........ Less, a rub with a rag!

David D

Stilldrillin · « **Reply #21 on:** February 23, 2012, 02:49:17 PM »

I finally got some meaningful workshop time, these past few days.

Modded the 12 tooth motor pulley, by boring to suit, and sleeving the boss o/d, to take an M3 grubscrew.

Needs a tidy up, and a shorter screw, but you get the gist of it........

Removed the flanges from the driven pulley. Faced, bored 10mm, and roughed the keyway......

Then turned away the large boss. The lathe was pulling like a train! Who needs speed reduction?

Filed the keyway. Installed nicely, inside the new recess in the bearing spacer......

Tried the new cradle mounting idea, on the old motor........

Time to remove the motor to swap pulleys, and cradle.

Ah! Whaat!

Perhaps this is why the motor's a bit noisy.........

Bugga!!!!!!!!

The new(ish) motor is 11mm longer in the plastic brush housing end.

I knew it was a neat fit inside the bed casting. But not to cause damage.....

No problem! I'll just swap ends!

No I won't! Not compatible, at all.........

BUT...... That wasn't the end of it!

As Dave BC had fixed the blown board. Bless Him!

There must be nothing wrong with the old motor, except the cracked fan blade.

This will suffice, until I can get the broken motor replaced.

Swapped to the old motor.

Switched on. With speed controll set at zero.

It took off at full revs, then stopped with a POP!!!

We've been here before, haven't we.............

Walked out. Locked up. Went and had me tea. And a real good good sulk........

Sigh.........

David D

Bluechip · « **Reply #22 on:** February 23, 2012, 06:48:44 PM »

Strewth. It is a bit moth eaten isn't it ???

Commutator looks none too healthy anyway. All that black ... er... whatever it is ... doesn't seem right.

The old motor looks better, just a dark smear where the brushes bear on the copper is about normal.

Oh dear ...

Oh dear, Oh dear Oh dear ...

BC

lordedmond · « **Reply #23 on:** February 24, 2012, 03:21:25 AM »

Dave I have to agree completely with dave BC on the condition of the comms the old first duff one looks just about perfect but the new duff one is well ugly not fit for man or beast.

but it could be many things bad neutral or wrong grade of brush , we used to aim for a nice shiny chocolate colour, it also relates to the load on the motor

Stuart

Stilldrillin · « **Reply #24 on:** March 06, 2012, 06:11:12 PM »

Well..... Finally got this job sewn up! (All bein' well).......

Dave Bluechip called this morning, with some test equipment, and also returned my original, repaired board.
There's nowt wrong with either motor. Electrically.......... Which was a bit of a surprise!

Therefore the intermittent fault must lie inside the 8yr old control box. Fortunately, I bought one from Amadeal a few days back!

It's a bit larger than the original Chester box........

So, two more M5 mounting holes were drilled, higher up the casting........

Nice new 400w motor, from Chester........

Getting to be a bit of a mongrel, now.........

I ran the motor for a few minutes, to bed in a little, then checked rpm. Low gear, 800rpm. High gear 1800rpm. That'll do for me!

Only had time to face a piece of 1" steel. It performed beautifully! When really heavily loaded, it just 'dug in', and kept going!

Rather pleased! Thanks everyone for your input....... Especially, Mr. BC!

David D

John Swift · « **Reply #25 on:** March 06, 2012, 07:16:02 PM »

Hi Dave,

It may be a bit of a frankenstein machine ,but it looks good to me

your picture answers a question of mine , how they fit the tacho into the control box
its easy , make the box is bigger !

John

Stilldrillin · « **Reply #26 on:** March 07, 2012, 06:38:17 AM »

Hi John.
Thanks for that!

The readout gubbinses are fitted in the bottom of the box. (Right hand end, here)......

Just below where the leadscrew passes through!

I've fitted an angled piece of plastic under the screw, to keep it from rubbing the wiring........

Incidentally, the new belt arrangement is blummin noisy! Would a shot of WD40 do any harm?

David D

Bluechip · « **Reply #27 on:** March 07, 2012, 07:03:23 AM »

Used to use Lubriplate # summat, can't remember, on timing belts.

Instinct says not wildly excited about hydrocarbon solvents on ( probably) rubber.

So,

Margarine, Hand cream, pork dripping etc. etc. should not do much harm.

Dunno really, helpful eh??

BC

PS Low cholesterol marge of course

lordedmond · « **Reply #28 on:** March 08, 2012, 02:53:16 AM »

talc powder will quieten it down a bit

PekkaNF · « **Reply #29 on:** March 08, 2012, 03:43:42 AM »

Quote from: Bluechip on March 07, 2012, 07:03:23 AM

Used to use Lubriplate # summat, can't remember, on timing belts.

Instinct says not wildly excited about hydrocarbon solvents on ( probably) rubber.

So,

Margarine, Hand cream, pork dripping etc. etc. should not do much harm.

Dunno really, helpful eh??

BC

PS Low cholesterol marge of course

Agree, I would not use antything that is not intended to this use. Some belts have rubber and some polyurethane, they hate different lubricants. Some handcreams render some plastics spongy and frail. Tooth belts will cause noice, specially at high speeds. Also wrong belt tension can cause all sort of problems.

PekkaNF

Stilldrillin · « **Reply #30 on:** March 08, 2012, 06:37:07 AM »

Hmmm...... Thanks Chaps!

I think I might have it set a little tight. Will ease it off a bit.......

David D

PekkaNF · « **Reply #31 on:** March 08, 2012, 09:25:13 AM »

I hope I don't sound here like I pretend to know something about this, because - quite frankly - I don't. However this is what I know:
* too loose and the belt will whip, too tight and it will whine
* I have broken pretty good size journal, because I was tightening the belt drive by ear. There was really little difference between "pretty good" and "even better". This even better worked for three years and then shaft bore next to cogged wheel.....
* One company recommeds hand thightening it and then further tightening of 0.4% of wheelbase. I.e 4mm per every metre of the centre of the shafts. This is on pretty high spec linear drive....rotary ones we use Trummeter.

I found this one, where is some info on pages 22 on, but if you don't have this info then it is only mildly interesting.....
http://www.mulco.net/content/en/download/res/34298-1.pdf

PekkaNF

HS93 · « **Reply #32 on:** March 19, 2012, 08:10:00 AM »

out of interest did you ecer check the RPM of the motor free running ?

Peter

Stilldrillin · « **Reply #33 on:** March 19, 2012, 08:29:51 AM »

Quote from: HS93 on March 19, 2012, 08:10:00 AM

out of interest did you ecer check the RPM of the motor free running ?

Peter

No, Peter.

There's only a pifflin' little shaft on it. Very little room to stick a reflector........

David D

HS93 · « **Reply #34 on:** March 19, 2012, 10:33:15 AM »

OK thanks

Peter

Stilldrillin · « **Reply #35 on:** March 19, 2012, 01:39:16 PM »

Managed an hour or so in the workshop, this aft!

It's been a long time, but I've been a good boy, and finished all the upstairs spring cleaning.......

Realised, I should check the belt tension. Someone said, should be able to comfortably turn the belt to 90*, mid longest run. All was ok.

While I was in there, I stuck some reflector tape on the pulley.........

I got some interesting results.

Running free. Forward, 4940rpm. Reverse, 3585rpm.

Belt attached.
Low gear. Forward, 5085rpm. Reverse, 3760rpm.
High gear. Forward, 5190pm. Reverse, 3860rpm.

Machine spindle. High gear, 1850rpm. Low, 790rpm.

So...... The motor runs around 100rpm faster, when driving the spindle. And 100rpm faster still, in High gear!

It's all a mystery to me........

David D

loply · « **Reply #36 on:** March 19, 2012, 05:49:39 PM »

David,

It's the motor speed controller, it supplies more power to the motor when it thinks it's needed.

Not sure exactly how it knows when the motor is bogging down but when it does it cranks up the juice.

Unfortunately the mechanism is evidently a touch crude - aside from what you've noticed it also creates an anomaly if you bog the motor down somehow (say by taking a deep cut) then it suddenly cuts more freely, the motor will over-rev before settling back down to the original speed.

Particularly noteable if you turn the variable speed right down, because it essentially turns it back up when it feels the need

Generally works well though.

Stilldrillin · « **Reply #37 on:** March 19, 2012, 06:54:38 PM »

Loply.
That speed controller is a clever piece of kit, if it knows the belt is fitted, or not!

I have noticed the momentary over revving, after heavy cutting.

Another puzzle, to me....... Motor spinning free, takes some seconds to come to a standstill, at switch off.
Belt connected. Despite the inertia of the chuck etc. It brakes quickly to a standstill......

These things are a bit more sophisticated than we take them for!

Anyroad! No more flashin' and poppin'. Working well, with much more torque available than before.

Thanks for posting your down gearing instructions....

David D

HS93 · « **Reply #38 on:** March 19, 2012, 07:26:27 PM »

That information will help me greatly in the conversion of my mill , it uses the same motor and I am going to remove the gears as I don't need low speed and just have a belt drive that should get rid of the noise. Ill use just under 2 to 1 so will get about 3,000 plus max rpm.
thanks again

Peter

loply · « **Reply #39 on:** March 21, 2012, 05:09:39 PM »

Quote from: Stilldrillin on March 19, 2012, 06:54:38 PM

Loply.
That speed controller is a clever piece of kit, if it knows the belt is fitted, or not!

Hi David,

Yeah it is quite clever.

I'm not sure if it senses the amount of current being drawn or if it uses feedback from the digital tacho, or both, but I did once observe that my motor behaved odd when I disconnected the tacho. Perhaps it was just a coincidence though as I would suspect the current monitoring option is more likely.

Stilldrillin · « **Reply #40 on:** March 21, 2012, 05:17:26 PM »

Loply.
My tacho has no means of sensing the spindle revs, as the original machine does not have that feature. The read out stays at 0, whenever the machine is live........

I guess it must be current monitoring.........

David D

John Rudd · « **Reply #41 on:** March 22, 2012, 04:28:33 AM »

David,

I Dont know what happened to my orignal reply that should have appeared some posts further back.......

Anyhoo....Current monitoring is done by the big white resistor shown in post 26 of yours...The controller looks very much like one from KB controls..maybe the KBIC240? and no the tacho plays no part at all in the speed control of the motor...Shame you cant make use of the readout...although nothing is impossible..You could buy the sensor from one of the suppliers and add it as a retro fit...

Stilldrillin · « **Reply #42 on:** March 22, 2012, 04:37:54 AM »

Thanks John!

Don't need a readout.
Like when driving my car. (Apart from restricted zones). If it feels ok, then it is ok........

David D

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Author Topic: Mini Lathe Speed Reduction....... (Read 33995 times)

lordedmond

lordedmond