Mini lathe transmission replacement

[loply]

Haha, what the?!

Thanks for the advice folks.

The lathe is a RealBull 7x14 (or is it 8x14?) quite a recent one and it's the kind that changes the power to the motor as required to keep it spinning.

Interestingly, I discovered yesterday that the tachometer is providing feedback of some sort to the motor controller... I had the tacho disconnected and the motor wouldn't run properly, randomly speeding up and down and not reaching full speed. With the tacho reconnected, instantly fixed.

On close inspection I am fairly certain that the gear selector fork was so badly made that it engaged itself with the gear teeth. It is free to rotate back and forth on the shaft by about 10 degrees (even if you don't touch the shift lever), and the fork is then free to 'wobble' side to side by another 10-15 degrees. The end result is that if the angle is just right you can take one of the 'legs' of the fork and jam it into the teeth of the gear!!! The angles are such that it jams inwards instead of being pushed outwards...

Well, clearly if the fork happens to vibrate it's way into that position during running... Self destruction occurs.

One of the legs of the fork has signs of damage/wear on it and some of the teeth on the gear look like they have been gouged.

I don't know if this lathe has overload protection or not, I'm hoping it does, but in either case what I have done for my 'fuse' is as follows:

The pulley on the motor output shaft originally was keyed to the shaft, and also had a grubscrew to prevent the pulley moving back/forth on the shaft.

I have removed the key and made a new, very small, grub screw with a tapered point which is just-so that it engages in a matching hole on the shaft. Only a small amount of the grub screw engages in this hole, and the hole is drilled over-depth by quite a bit.

My intention is that in the event of a serious overload or crash the grub screw will shear the end of it's tapered point off, and the point (or remains thereof) will have room in the over-depth hole to rest in peace.

I'm aware that I've put the 'fuse' on the wrong 'end' of the transmission here, as it should really be at the torquey end rather than the motor... However, I'm willing to take a risk on that.

If the grub screw doesn't sheer it's point off, the drive belt will hopefully snap.

As for overloading the electrics... I would have though down gearing the motor so it doesn't stall might help matters? The original setup meant the thing stalled randomly all the time, and the noise of the motor struggling when it stalls was never good... I would have thought stalling was the killer of electric boards...? Either way as expressed in my original post I view the electrics as a weak point anyway and may wish to bypass them at some point... I have heard of many people having electric boards blow for no apparent reason...

I used to own a PC repair shop and I know the vagaries of cheap mass produced electrics quite well. 5-7% of brand new computer products dead on arrival? Cheap electrics are the devils work.

[Bogstandard]

I thought this forum was called Mad Modder for a reason. Or should it be change it to Cautious Modder,

Actually, this site was originally brought about as a place where people could discuss and show the various projects that they are involved with, be it knitting or making a motorcycle. Nothing really to do with engineering at all.

It just so happens, and in my view, detrimental to the site, as many of the original great contributors have been driven away by it, that model engineering has come to the fore, making it just like any other run of the mill engineering site, with very few new innovative projects being shown.

Have a look at John Hills or Powder Keg's posts for example. THEY are what Modders was originally intended for

It was never meant to be 'ask a question topic and get an answer' site, the questions were asked within the topic that the specialist was showing. You actually took a deep interest in the projects that were being shown. You helped if you could, but marvelled at the ingenuity that was being shown.

I was one of the first model engineers to actually show what I was getting up to on here, and I now regret almost every topic I posted, purely because it has now come to this, where almost every post is about model engineering or someone asking how to do something or what should they buy. Not what the site was originally envisioned to be.

As to the cautious Modder.

If members don't take safety as a first priority, then they should NOT be posting on here and making dangerous topics public. Safety is paramount in everything we do, risk takers, in my opinion, should have no allotted space on such a public site as this, and at the first sign, should be given a one and only warning of it, and the offending material removed. Do it again and you are out of here.

But of course, I was asked to become a mod, many moons ago, almost at the start of the site, but I am too volatile to be one, so I refused. I have no say in how the site is run, but I hope that someone in the upper echelon, in their wisdom, will see that I am talking sense.

Enough accidents happen in what we do without adding more fuel, causing further ones.

And just a thought for all

Accidents don't happen, EVERY one has a reason or cause.

So yes, it should be Cautious Modders.


Bogs

[loply]

Bogs, with all due respect none of the above relates to me or this post.

I don't intend to make models and I've only posted about twice on this forum.

This post was about modifying a mini lathe to install a whole new transmission system. Not exactly 'mad' or incredibly novel or interesting but I think it's in keeping with the ethos of this forum...

I don't see what you're getting at though, Once I have my lathe working maybe I'll make something you can marvel at!  

[spuddevans]

Ok folks, this thread is getting dangerously close to being locked for 2 reasons, 1, there are a quite a few off-topic posts that, while in themselves making valid points, have nothing to do with the subject, and 2, a confict of personalities seems to be arising that could easily lead to flaming.

Any more off topic posting or comments that appear to incite others will result in all bar the original on-topic sections of posts being edited/deleted. I have already edited some of the comments deemed to be out of keeping with the "Friendly" nature of this forum.

If there is any of the (still-remaining) off-topic posts that you want to comment on, it would be best to start a new thread about it in the "Water Cooler" section ( or the appropriate section within the forum ) so as to keep within the original poster's points and questions.

Let's keep it civil, or better yet, friendly.


Tim

[DaveH]

Tim,

I agree 100%

DaveH

[Andrew_D]

I did exactly this type of mod to my 7x12.

Spindle extension off the left hand side holds a 4-step pulley and still allows up to 5/8" shaft to pass through. That was tricky....left hand internal metric thread to cut so that it screws onto the spindle....

Another 4-step pulley on a jackshaft mounts on the rear of the lathe. This jackshaft is driven by a treadmill motor through a 1:5 reduction belt drive.

The treadmill motor is powered via a DC-controller I found on EBay. Some type of obsolete industrial control. Took a bit of work to find out the specs and jumper settings for it, but the company was quite helpful.

I don't have any pics, I'll see if I have time to take any later today.....


I'm thinking of giving the old girl a cleaning up, but not sure how far to take it...tapered bearings? longer bed? Also the tailstock is very stiff. I think the tailstock spindle got bent, or the casting is buggered somehow. Was thinking of taking off the tailstock and carriage and making a small turret lathe...so many ideas, so little time and money....

Andrew

[loply]

Andrew, how long was the spindle extension and are you confident that the drive force being exerted a few inches away from the spindle bearings isn't creating any unwanted imbalance? I'm concioua that any misalignment of spindle extension or pulley bore will result in a washing machine lathe 

Although it's overly complex I'm actually pondering a belt driven layshaft in the location of the original motor whereby two belts can be selected by means of a motorcycle gearbox type dog system, the reason being that I would end up with two gear levers (including the original one) in approximately the same place on the back of the headstock for a nice quick change system, and could have ratios with max speeds of 145, 380, 680, and 1000rpm... Exactly the kind of range I want!

First just getting the head rebuilt and my DRO fitted though...

[John Hill]

Have a look at John Hills or Powder Keg's posts for example. THEY are what Modders was originally intended for

           

[Andrew_D]

Andrew, how long was the spindle extension and are you confident that the drive force being exerted a few inches away from the spindle bearings isn't creating any unwanted imbalance?

Never thought too much about the extra side forces to tell the truth. 

I had a look at the ol' girl today...it actually was a 3-step pulley. This gives 1:2, 1:1, 2:1 ratios (relative to the jackshaft). The jackshaft is 1/5 the motor speed.

I took some pics, but am currently trying to put kids to bed, so will check back in a bit...

Andrew

[Andrew_D]

Here's some pics...

The piece that screws on to the spindle is actually three pieces. The 3-step pulley, a piece of round tube/pipe, left-hand thread nut.

I had to make a replica of the spindle thread first using one of the original nuts as a go/no-go gauge. (Before removing the gauge from the chuck, I marked where jaw #1 was...see why later.) Once I had the piece threaded, I made the nut and threaded it, using the go/no-go gauge as I cut the thread. I milled some slots in the nut to provide a means of tightening. (Similar to the original nuts actually.) This nut was then welded to a piece of thick-wall tubing. The go/no-go gauge was chucked back up thanks to my marks made before and the nut/welded tube was screwed on. A couple light facing and turning cuts to square things up. The center was then bored out to about 1" if I remember correctly. The nut was removed from the go/no-go gauge and the gauge removed from the chuck. A hole for a set screw was drilled and tapped in the side. Now the pulley was chucked up. In the end of the large pulley, it is recessed. (Cheap buggers couldn't leave THAT much aluminum behind!!!) The center was a hair over 1". I turned it down slightly until the welded nut slid on about 1/8". I then took the pulley & welded nut over to my horizontal press (big vise!) and slowly pressed the two together with some red loctite. The set screw was also added for extra holding power.

Nothing special about the frame work holding the jackshaft. Some 2" x 1/8" wall tubing extended back from under the base. (I had made two lift blocks out of this tubing earlier to raise the lathe up off the bench, so this frame work simply replaced the headstock lift block.) The jackshaft bearings are mounted on some 6" x 3/8" plate, hinged at the bottom. A simple tensioner keeps the belt tight.

The motor hangs off the top rear of the jackshaft plate. Another simple tightening bolt here too.

The numbers, as mentioned earlier....the pulleys provide 1:5 from motor to jackshaft, then 1:2, 1:1, 2:1 to the spindle. The motor is 1.5 HP continuous duty @ 95 VDC, 2.5 HP treadmill duty @ 130 VDC, 18.5 Amps 6750 RPM. This gives the motor a range of 0-6750 RPM, the jackshaft is 0-1350 RPM, and the spindle is 0-675 RPM, 0-1350 RPM, 0-2700 RPM. The motor is run with a obsolete industrial control I found on EBay...much better than the original motor and controller!!!!

Andrew

[loply]

That's a beast  2.5hp?

You'll have to be careful not to snap the bed in half!

I don't think mine will be quite so industrial.

How did you find it cuts now with the new setup? Have you done much low speed parting?

[Andrew_D]

That's a beast  2.5hp?

Well, that's 2.5 "Chinese Treadmill" HP...I don't think it's anywhere near that when converted to "normal" HP! 

How did you find it cuts now with the new setup? Have you done much low speed parting?

Cuts like a dream. Parting, threading, etc....no problem.
Unfortunately, I don't use it too much as my big 20" x 48" sits beside it. (7.5HP, Canadian made, WWII vintage.) 

Often small parts still get made/fixed on the little 7x12 though. It's just so handy to get right up close to those small parts when they are being worked on. That's why I'm thinking of fixing her up a bit.

It'll have to wait until the radial drill project gets back together though. (http://www.practicalmachinist.com/vb/antique-machinery-history/american-tool-works-radial-arm-drill-209283/)

Good luck with your project and keep us informed!!!

Andrew