Breaking drive belts on super mini

[andrew lynerParticipant @andrewlyner71257]

[andrew lynerParticipant @andrewlyner71257]

I have a Warco Super Mini lathe and I have just bust my second drive belt. The first one lasted longer than the recent one. I though I had learned how to treat it right but obviously not! It os starting to get expensive.
I thought I had sorted out the digging in problem when parting off by using copious paraffin from a brush when parting off but this afternoon (it would have to be Saturday) it stuck and there was the 'scream' that sounds like the drive wheel running under the slipping belt. You can hear the sound of damage being done.

When I replaced the belt I looked for a motor adjustment for belt tension but couldn't find anyone the vicinity of the motor. Has anyone had this problem and is there anything I can do about it? Could it be too slack?

The belt is actually quite flimsy and replacing it takes an annoying length of time. Buying one from Warco is expensive and a cheaper source would also be handy to know about. But basically I'd appreciate tips for ways of avoiding having to put in a replacement.

[not done it yetParticipant @notdoneityet]

You have no profile entry, so difficult to suggest a local supplier. I use ABC for all my belts and mostbearings.

Plenty of belts available from lots of suppliers on the ‘net.

How about arranging for the motor to trip if it is overloaded?

[andrew lynerParticipant @andrewlyner71257]

I must update my profile (I live in West Essex aamof) but I haven't found anywhere local for these things. I mostly use eBay for bits and bobs but I don't know how to specify a belt and the ones I have seen seem to be only 8mm wide for mini lathes. Mine is 10mm wide.

I did try on e enquiry but he said he couldn't help me.

The idea of an electrical cut-out is attractive. I was wondering how to detect a speed drop that would operate faster than the simple rev counter that's on the machine already. There is probably a good mod that can be done on the brushless motor control directly.

I would like to know how to avoid jams better in the first place, though. I am, much better at parting off these days. I make sure the carriage is locked down, the gibbs strips are not sloppy and I regularly sharpen the blade. It may be I am too chicken to run at a fast enough speed, perhaps.

[Jeff DaymanParticipant @jeffdayman43397]

How wide is your parting blade? a narrower one will reduce load on your belt.

If parting is the only op that strips your belts it might be wiser to use a hacksaw or portable bandsaw to part off. Use a saw only with the lathe stopped, for safety. No shame in parting by sawing . If using a saw in the lathe take a bit of time beforehand to make a wood or sheetmetal guard for the bed below your cut, in case saw breaks or drops through the cut unexpectedly.

If you are stripping belts on other ops you may need to think about getting a second much bigger lathe!

[HopperParticipant @hopper]

Have you tried running the parting tool upside down so the chips fall out (with lathe running in reverse of course)?

Carriage and topslide locked in position while parting off?

[David George 1Participant @davidgeorge1]

Hi Andrew when you are parting off using a part off tool in the normal toolpost it puts a stress on the slides and ways as the force is trying to rotate the toolpost. The usual part off toolholder sticks out to the side and gives a slight more rotational force and if any play it multiplies the force as it grabs. If you have a rear toolpost with tool upside down,for parting off, the force is contained within the main carriage with no chance to twist the toolpost and then grab. Does this help, in a larger lathe it is much more sturdy so less of a problem.

David

Edited By David George 1 on 18/11/2018 07:03:53

[jann westParticipant @jannwest71382]

on the topic of parting off … parting off tools can be very finnicky about being 100% dead on perpendicular … even a little out and the deeper you go the more you rub on the side. Also, topslide rigidity is a concern in minilathes!

[Brian GParticipant @briang]

It sounds like your belt is way too slack (especially if you can fit it without adjusting the motor position). My son's machine had the same issue, with the belt slipping on deep cuts or parting off.

Unless anything dramatic has changed between Warco's mini lathe and super mini lathe, there won't be any adjustment mechanism visible when the motor cover is removed, as the motor slides up and down, rather than pivots. Remove the four screws holding the control box on the front of the lathe and move it to one side so you can see the motor bolts in their vertical slots. It is a couple of years since I did it but I am pretty sure I removed the motor cover at the rear as well in order to hold the motor when adjusting.

It is important to ensure that when you tension the belt the motor remains level or the belt will not run true on the pulleys. In the absence of any tensioning instructions I tightened it until I could just turn it 90 degrees, at which point there was no more resistance than turning the motor without the belt. Since then there has been no sign of bearing wear and no slipping, so that is probably about right.

Brian

[larry phelan 1Participant @larryphelan1]

Parting off ! The old foe,once again ! I find that the rear post does help a lot [most times ]

[SillyOldDufferModerator @sillyoldduffer]

My first thought was you're expecting too much of the lathe Andrew. Parting off is notoriously difficult and it's harder to do on small light machines than big heavy ones. But snapping a belt is unusual, and breaking two suspicious.

On second thoughts, I wonder if you've got a combination problem:

• A tendency to be heavy handed when parting off, perhaps with a broad blunt tool not quite set at the optimum height. This one is fixed by experiment and practice, but my mini-lathe was never 'good' at parting off. It's much easier to do on a bigger machine with a rear-mounted tool-post.
• A maladjusted belt : I think this is a distinct possibility, with two causes. The belt on my mini-lathe was adjusted by moving the whole motor. Slots allow the motor to be moved to both tighten the belt and adjust the angle and relative position of the pulleys. By loosening the bolts slightly the motor can be fine tuned. When correctly positioned, the bolts are tightened. It's a simple system made difficult because the bolts are awkwardly placed behind the motor and approached from the rear. If you're not familiar with the job, it's very easy to end up with an incorrectly tensioned belt (too tight or too loose) plus pulleys misaligned slightly in both position and angle. The effect on the belt is slippage and/or rapid wear. Worn belts are most likely to break when asked to do an unusually heavy job like parting-off.

The website is down at the moment so I can't provide a working link or check it makes sense but I think http://www.mini-lathe.com has a good description of how to adjust the belt.

Dave

PS I see while I've been typing slowly and slurping coffee that Brian got in first with the same point.

 

Edited By SillyOldDuffer on 18/11/2018 09:50:47

Edited By SillyOldDuffer on 18/11/2018 09:53:31

[andrew lynerParticipant @andrewlyner71257]

Thanks for all the responses. Of the possible causes, I don't think it's my being heavy handed as I am on the timid side. I get the blade well lined up at right angles and re-adjust the compound on the go, to stop the blade touching the sides. It's a narrow blade, of course and it cuts very convincingly when it does cut. It really could just be failure to clear the swarf. This last time, there was a really solid ball, jammed / welded in the slot which I had difficulty clearing manually – going in alternate directions until it loosened. The speed was only about 350rpm. An upside down blade may help me out and I can easily try that at no extra cost(!).
Changing the tool post sounds like a plan. Presumably fitting a rear post just involves tapping a hole in the cross slide. There will be an optimum position I guess.
I'll have to look at motor position adjustment. Motorcar fan belts always have a recommended free movement but, in the absence of a specified setting, I guess the best setting would be with as little slack as possible, consistent with no static load on the bearings. Getting it square shouldn't be too hard. Hearing the teeth of the belt rattling over the teeth of the sprocket certainly doesn't sound right. From the above comments, I take it that it's not a common sound from minis. I must say, the belt seems very flimsy and not much tougher looking than a 'Hoover beater' belt. There will be a fair bit of torque on a 450W brushless motor. Why not a chunky Bee belt? But you will all say "Why not a chunkier lathe?" lol.

[andrew lynerParticipant @andrewlyner71257]

Posted by Brian G on 18/11/2018 09:11:48:

It sounds like your belt is way too slack (especially if you can fit it without adjusting the motor position). My son's machine had the same issue, with the belt slipping on deep cuts or parting off.

Brian

The belt was tight enough to need to remove the top sprocket to fit it. But I will still address the tension problem.

I was searching for info on rear tool posts and came across this link. There are some valid sounding arguments against mounting tools in a way that lifts the cross slide off the bed. I shall investigate height and angle of the cutting face

[SillyOldDufferModerator @sillyoldduffer]

A few comments Andrew:

• Re 'timid'. I once worked with a chap who stripped dozens of threads on RS232 plugs whilst installing VDUs. Turned out he was ex-combat engineer who defined 'delicate' to mean not putting an extender on a spanner and hammering it. He was an expert on building Bailey Bridges and other robust engineering, and had trouble turning the volume down. On the other hand, being too gentle is also bad. If the tool rubs rather than cuts, it will blunt, get hot and perhaps weld.
• What sort of parting blade are you using? If HSS, 350rpm may be too fast.
• "last time, there was a really solid ball, jammed / welded in the slot which I had difficulty clearing manually". Been there, done that! The welding part implies it got very hot rather than cutting. Blunt tool, wrong height, insufficient lubrication, or swarf failing to clear and being minced continually between tool edge and work.
• 'The belt was tight enough to need to remove the top sprocket to fit it.' That might be a clue to the breakages. My method might be wrong, but I think you're meant to adjust the belt and tension by moving the motor, not by removing a sprocket. That may have badly strained the belt due to excessive leverage on re-assembly. Can someone more knowledgable comment?
• "I must say, the belt seems very flimsy". I doubt that's the problem, belt snapping isn't a common problem on mini-lathes.

For what it's worth, I found parting off on a mini-lathe to be a challenge to the extent I avoided doing it unless essential. The lathe was OK parting off brass, but Aluminium and Steel both needed extra care in different ways. As the lathe is light and bendy, parting off requires the operator to have good judgement. Fortunately for foolish old me, quite often it wasn't a problem to remove the job from the lathe, saw it, and then pop it back on the lathe to tidy up.

Parting off is much easier to do on a heavier lathe. Upgrading to a WM280 reduced my front-post parting-off failures by at least 90%. Fitting a rear tool-post, which is easy to do because the saddle has T-slots, made parting off almost fool-proof. Now when it goes wrong, it's almost always obviously my fault. (Like optimistically cutting a bendy rod too far away from the chuck.)

Dave

[Neil WyattModerator @neilwyatt]

I'm not familiar with the adjustment on the Warco Super Mini, assuming that (a) you have a toothed belt and (b) its similar to other mini lathes, then adjustment is by moving the motor. Some machgines have a push-puill arrangement fo screws under the headstock, but the super mini may be different.

The screeching is the toothed belt slipping and this will rapidly degrade both belt and any nylon pulleys.

You need to get the tension so high you can just twist the belt 90 degrees between finger and thumb.

If the motor pulley is worn, you may be able to extend its life by reversing it though spare should be available.

If the tension and pulley alignment are good then the belts should last several years of frequent hobby use.

Neil

[Neil WyattModerator @neilwyatt]

Posted by andrew lyner on 18/11/2018 10:56:04:

Thanks for all the responses. Of the possible causes, I don't think it's my being heavy handed as I am on the timid side. I get the blade well lined up at right angles and re-adjust the compound on the go, to stop the blade touching the sides. It's a narrow blade, of course and it cuts very convincingly when it does cut. It really could just be failure to clear the swarf. This last time, there was a really solid ball, jammed / welded in the slot which I had difficulty clearing manually – going in alternate directions until it loosened. The speed was only about 350rpm. An upside down blade may help me out and I can easily try that at no extra cost(!).

Depending on diameter 350rpm sounds high for HSS.

Being timid is the main reason for people having failures with parting – the tool chatters, the instinct is to reduce the infeed and it rubs then blunts or grabs and…

Better to keep the speed modest and the infeed nice and steady – have confidence. This is true of all sizes of lathe.

Don't move the blade sideways while cutting, that's a real recipe for a dig-in. If you want to do this retract the tool before moving it sideways.

Neil

[andrew lynerParticipant @andrewlyner71257]

Posted by Neil Wyatt on 18/11/2018 16:21:17:

The screeching is the toothed belt slipping and this will rapidly degrade both belt and any nylon pulleys.

Neil

Luckily, the sprockets are steel.
I will deal with the adjustment when the new belt arrives.

I know there's no shame in using a hacksaw but parting off is something I'd like to be capable of but not at £20 per failure.

[andrew lynerParticipant @andrewlyner71257]

@Neil "Don't move the blade sideways while cutting, that's a real recipe for a dig-in. If you want to do this retract the tool before moving it sideways."

I only move it to stop it from drifting to the side of the cut. But where is the drift coming from if the carriage is locked and the blade is square on? (I ask myself. – there's a lot to learn here, I think.)

[mechman48Participant @mechman48]

Obvious questions but; have you got the tool on centre height, do you have enough back rake on your tip ( HSS ? ) so that the swarf 'curls' up & out of the slot. you say you have paraffin as coolant, are you parting off aluminium in which case you need to up your rpm as 350 rpm will heat up the aluminium & make it stick. Not having a mini lathe ( I have a WM250V-F ) I assume that there is no auto X feed & you are feeing in by hand, can you 'feel' what the tip is doing, you should be able to 'feel if you are feeding in too fast / slow… adjust accordingly.

I have my compound slide pulled back toward the centre of the X slide so to have better support under the overhang & with all the locking bolts on the saddle pulled up, as you have, plus I have a lock on the gib strip…

Tool holder / compound slide set back so that overhang is better supported over saddle…

George.

[Ron LadenParticipant @ronladen17547]

Andrew,

Though it is no consolation you are not alone, I think most beginners go through this when they first try parting off, I certainly did. My CJ18 lathe is pretty much the same as your machine except mine is not brushless and it currently has no low gear range, I only have the top range. I had a couple of stalls when parting off and the second time the low gear change wheels which are nylon gave way. I still have to get replacements and fit them, something I am not looking forward to as the head needs to be stripped down.

Its a while since I did any parting off but I did get to a stage where I was reasonably ok with it. Like most beginners I guess I was just too timid, taking tiny cuts and hesitating at every change in sound or the slightest hint of chatter. Then some of the guys here on the forum told me to keep cutting, keep feeding into the cut, dont go mad but keep cutting and that did work for me. I think once you have had one or two failures it does knock your confidence though which makes you nervous and hesitant the next time you do it. At the end of the day Andrew I guess all we can do is keep at it and learn from what works and what doesnt and hopefully it will come together.

Ron

[Martin ConnellyParticipant @martinconnelly55370]

Here's a calculation to consider. If you cut at 0.005" per rev how fast does the tool have to move in at 350 rpm. Are you going anywhere near this speed? 200 revs requires a movement of 1" in just over 34 seconds. If you are not power feeding then this is whst you need to consider when turning that handle.

Martin C

[Neil WyattModerator @neilwyatt]

Posted by andrew lyner on 18/11/2018 16:29:47:

@Neil "Don't move the blade sideways while cutting, that's a real recipe for a dig-in. If you want to do this retract the tool before moving it sideways."

I only move it to stop it from drifting to the side of the cut. But where is the drift coming from if the carriage is locked and the blade is square on? (I ask myself. – there's a lot to learn here, I think.)

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.

[andrew lynerParticipant @andrewlyner71257]

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.

[Martin ConnellyParticipant @martinconnelly55370]

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

[Ron LadenParticipant @ronladen17547]

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

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