Breaking drive belts on super mini

Is it a sharp, square-ended tool? If it has an angle end this tends to pull it along.

You may have the saddle gibs set a bit loose?

Also, if you can disengage the leadscrew by putting the forward/reverse tumbler in its mid position, engaging the leadscrew half nut(s) can help prevent the carriage from drifting.

So many questions and so many points. Where to start?

The tool post is fixed at one point on the cross slide - no T slots so no adjustment of position is possible.

I keep the tool sharp with some relief on the top. I try to have the edge square on and noticed that an angle can pull it to one side.

I didn't understand the calculations about feed rate and cutting speed in the context of parting off. 300rpm is too fast? It took me a while to understand that there is an optimum speed and that I had been going too slowly and I also only recently found that I can quite happily cut at least 0.5mm along an Aluminium rod.This has allowed me to speed up work a lot. But parting off seems to require less depth and speed.
This is where my lack of background training gives me trouble.

This is all very frustrating because I haven't even had a chance to order a new belt yet. It's still only Sunday night.

Anyone who uses cnc has to consider depth of cut (also known as chip load or in the case of parting off feed per revolution). A typical figure for most jobs is 0.005" or 0.125mm. If you have a lathe with power feed on the cross slide this is the typical setting you would use for parting off as it will ensure continuous cutting and no rubbing. It requires some confidence as it seems far too fast to a beginner. You will see lots of posts where the advice is don't be timid.

With regards ti your problems, at 350rpm 200 revolutions will take 34 seconds. At this rpm in order to maintain a 0.005" feed per revolution you have to feed the tool in at 1" in 34 seconds to have a feed per rev of 0.005". If you are hand feeding at 350 rpm then any pause in feed runs the risk of the tool rubbing and not cutting, you need to keep the pressure on.

So the question is, are you power feeding or manually feeding? If power feeding at what setting? If manually feeding how fast? Without running the lathe try to turn the crossfeed handle to give 1" of movement in 34 seconds and see how it compares to what you were doing and let us know.

Martin C

Andrew,

I dont know if it will help but have a look at the Bearing Boys Ltd website, go into Transmissions at the top of the page and then Metric Timing Belts. You will need the number of teeth, belt width and the pitch, I dont know if they will have your belt or not but worth a look as their prices are really good.

Ron

p.s. Forgot to say Andrew, when you go into metric timing belts there will be four options re tooth pitch, once you have chosen your pitch, there will be a box on the left. Enter the number of teeth and belt width and if they stock that belt it will come up including price.

Edited By Ron Laden on 19/11/2018 08:18:31

Edited By Ron Laden on 19/11/2018 08:22:27

It would be useful to know the diameter of the work being parted off, a 10mm rod needs a somewhat different speed to a 100mm one. Also at the larger diameters you run the risk of stalling a minilathe if trying to take 0.005" DOC which will hopefully cook the belt before something more expensive.

J

PS Order two belts so you always have a spare ready to go.

PPS there are also the odd far eastern belt pitches which you won't get from the usual belt suppliers.

I managed to order their last two belts from Warco. (It hurt a bit). The belt is more flimsy than any I can find elsewhere. My sprockets are steel but I wonder if that belt size was chosen to protect nylon sprockets on earlier models (to be the weak link, perhaps). Anyway, I should be in business by tomorrow and I will adjust the tension. It will be interesting to find if the earlier catastrophe had managed to jerk the motor mounting enough to slacken it further - to account for the much earlier failure of the second belt. I will go into the shed and find that out soon.

On the topic of cutting rates, I only recently found that there is a speed and depth when turning a diameter that seems to settle down very convincingly - and it's deeper and faster than I would ever have dreamed of (having heard but not properly listened to the comments on YouTube) . The swarf seems to lift off very nicely into coils and the whole thing gets noticeably warm. The motor power is definitely doing its job. It's only when I disengage the power feed that the 'chattery noises' start and I have to pull the cross slide quickly. I guess I can translate that experience (with a cut depth of say 0.5mm) to a suitable speed for parting off with a 2mm cutting tool width. Plus the fact that, when parting, the speed across the surface will always be less as the piece gets thinner.

Not seen a Warco Super Mini myself so it is possible it comes fitted with an unusually weak belt. I think it unlikely to be the root cause because parting off is notoriously difficult especially for beginners, and triply so when they are cutting a difficult material on a small lathe.

Parting off is one of those operations where everything has to be 'just right' and this is hard to arrange. Particularly on a small lathe, it's likely that the tool won't be held straight if too much pressure is applied. Front tool posts bend (they do!), the work bends, saddles twist and lift on the gibs, and the saddle can be pushed along the bed. If any of these happen, expect a dig-in. Unfortunately it's also vital that enough pressure is applied to cut. If the tool is allowed to rub, it goes blunt, and the friction generates enough heat to soften the metal causing the tool to grab and another dig-in. This makes parting off a balancing act and - particularly on a small lathe - the onus is on the operator not to make any mistakes. Setting up requires all sources of movement to be minimised - lock the saddle, reduce overhangs, tighten the gibs, avoid worn lathes etc. Even after all these things are done, a rear tool post out-performs a front tool post because they are more rigid.

Then the operator has to know his lathe and the materials he's using so he can optimise cutting speeds, pressures, lubrication and swarf clearance. There are significant differences between alloys, I find brass always parts well provided the tool is sharp. Aluminium alloys are often bothersome because they can be sticky. I doubt there's anyone on the forum who's not had bad parting experiences.

One thing about the learning process that might help. Quite often people picking up new skills plateau - they get so far and suddenly can't improve no matter how hard they try. The cure is do something else for a while, and then have another go.

Although the belts are breaking during parting off, I think something else is damaging them. When you fit the new belt, it's worth double checking alignment as well as tension. Depends on how your lathe manages the adjustment, but changing tension might interact with alignment and vice versa. Getting everything trued up could be another balancing act.

The diagram exaggerates getting it wrong, but quite small misalignments between the motor and the headstock pulley can soon damage a belt. I suspect that, compared with ordinary types, a toothed belt could be extra vulnerable. If the teeth become stress raisers and there's a sideways tearing action I can imagine the belt quickly failing.

When the new belt is on can you post some photos?

Good luck,

Dave

Edited By SillyOldDuffer on 19/11/2018 12:15:42

.

Aside from the considerable cost to you, that ^^^ must be rather worrying for other owners.

MichaelG.

Rather depends when Warco are expecting new stock.

Assuming it is the 9.5mm wide 1.5x 70 belt, Amadeal, who also sell the Real Bull machines list them. Incidentally, the picture under "Bed for the mini lathe" on the Amadeal website shows the two slots by which the motor is mounted.

Brian

If the Warco belt is the same as the Amadeal belt, Amadeal,s price is £7.50, Bearing Boys price is £2.65, just shows how the prices get loaded.

Amadeal sell a brushed motor machine, the Warco Super is brushless and uses different belt arrangements.

Actually the Warco belt has 70 teeth and is 9.5 mm wide so they could be compatible.

But I couldn't find a direct equivalent on Bearing boys site; their stuff all seems to be more chunky. (Don't go making me feel bad about my running costs. I have enough trouble with my own conscience as it is. )

Lining up the belt is made easy by the fact that the clearance between the straight bits of the belt are only about 1mm away from the gearbox case. You can eyeball it pretty convincingly. The drive end of the lathe is getting to be my AK47 - I shall have to try to strip and assemble with the lights off . Problem would be finding the screws I always drop on the shed floor.

On the subject of dropping and finding things. The magnetic base of my dial gauge is fantastic. You can 'turn it off' and drop all the steel things right in their box. Because of that, it's better than my super magnet that I bought for the purpose.

A bit like saying the supermarket sells your favourite pint cheaper than your local.

Bearing Boys sell thousands of different belts a year, tool specialists probably sell a handful.

The economics of buying in and holding the stock are very different, bearing in mind that a wide range of spare parts need to be stocked yet some won't even sell one item a year.

Neil

I understand the reasons why Neil but I would buy my belt from Bearing Boys and that will leave me enough change to buy a pint in my local even at their prices...

Andrew,

I found the 70 tooth 5mm pitch belt though it is 9mm wide not 9.5mm but I cant see that a problem. How do you know their belts are more chunky..? unless I missed it they dont mention belt thickness do they..? If they are thicker would that be a problem, may be a good thing unless you are wanting a thinner weaker belt as a safety trip..?

Ron

Edited By Ron Laden on 19/11/2018 21:13:51

@Ron. I found the belt you refer to in the" timing belts" but I only got there by a circuitous root. Knowing one's way around can be a big help. Those belts are more like mine. Not chunky like on the other pages.