hobbymat not cutting Parallel

[jamie creightonParticipant @jamiecreighton58639]

so i finally got around to trying out my hobbymat lathe,i mounted it on 3 laminated boards of plywood and levelled everything up.

when i do some test pieces they all seem to be tapered,ie its taking more off the tailstock end than the chuck end.

what i mean as an example is it measures 56.6 at one end and at the chuck it goes up to 56.7mm.

ive ordered some more round bar to do the ring test so i can see whats going on but until then any pointers would be appreciated.

[jamie creightonParticipant @jamiecreighton58639]

[Howard LewisParticipant @howardlewis46836]

Is your test piece just held in the chuck, or is it between centres?

The chuck end being larger tends to rule out the test piece flexing, otherwise it would be oversize at the free end.

If between centres, it suggests that the Tailstock is JUST out of line

Another possibility is that the Chuck jaws are holding the bar just off parallell, (were / dirt?

If the bar is only held in the chuck, it suggests that the Headstock and Bed are fractionally out of line.

This assumes that the Cross slide gibs are set correctly, and that the Cross Slide was lockedi

Ditto for the tool post being locked, and not shifting at all.

Howard

[jamie creightonParticipant @jamiecreighton58639]

hi howard,

im not using the tailstock,i will have a good look at the jaws of the chuck,its a 4 jaw but i have the standard 3 jaw that came with the lathe so i can check it cutting agaisnt the 4 jaw to see if thats the problem.

all the gibs have been re adjusted but i must admit i didnt lock them off,the hobbymat has on the crossslide and the tool post slide a allen bolt that sits i between 4 gib grub screws,i guess that the slide lock?

i have cleaned out and re greased the main spindle bearings,would over tightening cause the spindle to not run true with the carridge? i did run the lathe for 30mins and check if the area around the bearings got hot but i will re check.

[Martin of WickParticipant @martinofwick]

A common issue with many posts for various lathes. Much has been said.

We assume you are not using a top slide and you are driving using the leadscrew and cross slide. You don't state length of cut.

You can check whether the problem is chuck or headstock with a decent length of silver steel say 20mm but it wont tell you whether the problem is with the chuck or headstock but unlikely to be chuck if you took a full cut (unless the piece moved during cutting in some strange wa.

You can check headstock alignment alone by purchasing a MT2 test bar six inch will do.

Good news is probably not bed wear if Dmax is at the headstock (unless the tailstock end appears untypically worn)

May be saddle is twisting slightly- check saddle gibs are tight and confirm it moves smoothly from head to tail without any loosening or tightening.

It might be some bed twist issues.

 

 

Edited By Martin of Wick on 06/01/2020 19:49:26

[JasonBModerator @jasonb]

You don't say over whet length you are testing or what material you are cutting but a 56mm dia bar in a small lathe will be putting a lot of load on it.

Have you preloaded the bearings as if too loose that would cause the far end to be larger.

Is tool sharp and on ctr height, if not both could be pushing the work away from the tool and giving the big end, particularly if chuck jaws are worn and bell mouthed.

 

Edited By JasonB on 06/01/2020 19:56:42

[OldironParticipant @oldiron]

IMHO the first thing to do is use a centre in the tailstock and recheck the measurements. A piece of 56mm material of more than a few Cms stickout is not going not going to run perfectly true in a 3 jaw chuck. Or run between centres and see how the results compare.

regards

[jamie creightonParticipant @jamiecreighton58639]

the 56mm was just an example figure,the bar stock was about 25mm and 120mm long.

[DiogenesIIParticipant @diogenesii]

Hi Jamie

When you check the alignment again, make sure that the saddle is correctly adjusted to allow free movement along the bed, but without free-play – this is critical to accuracy on the Hobbymat as it has a round bed. Use a centre in the tailstock, and lock both the tailstock and the tailstock quill, as well as the slides.

As Jason suggests, looseness of the headstock bearings will cause this issue – if you have run it for 1/2 hour since refitting them, I'd check this first – they do tend to settle in a after a little running..

[HopperParticipant @hopper]

Posted by jamie creighton on 06/01/2020 19:14:55:

i have cleaned out and re greased the main spindle bearings,would over tightening cause the spindle to not run true with the carridge? i did run the lathe for 30mins and check if the area around the bearings got hot but i will re check.

Did the lathe turn out of parallel before you removed the spindle and greased bearings and reassembled?

IF not, then the problem is most likely something in the reassembly.

Check the preload adjustment on the bearings again, they may have bedded in some with use. Also, check there is zero measureable up and down or side to side movement of the spindle where the chuck mounts. Do this test with a long bar held in the chuck to yank on, and a dial indicator resting directly on the spindle. With taper roller bearings, should be zero movement.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Jamie, I assume that there is no dirt or gab etc. between the chuck and the flange on the spindle. I think if you have a bit of 25mm bar 120mm long held just by a normal 3 or 4 jaw chuck and no tailstock support, it is a big ask, as you are only holding by the end of the jaws, assuming you have the normal size ones for a Hobbymatt.

Just in case you don't have the information about the spindle bearing preload, below is a scan of the instructions for adjustment.

I'm also assuming that the flange has not been unscrewed from the spindle at anytime or during disassembly, as the instructions strongly recommend not too.

Regards Nick.

[DiogenesIIParticipant @diogenesii]

Nick, as a matter of interest, do your Clamping & Forcing Screws 5 & 6 actually conform to the last illustration? ..only asking because mine are the opposite way round to that..

[jamie creightonParticipant @jamiecreighton58639]

mine are too,the middle hex bolt is the forcing one

[DiogenesIIParticipant @diogenesii]

Thanks for clarifying..

[jamie creightonParticipant @jamiecreighton58639]

just to say thanks for all the help fella's.

i will give it a good check over at the weekend and report back

[Nicholas FarrParticipant @nicholasfarr14254]

Hi DiogenesII, yes mine are exactly as the illustration is, but I believe mine is an early model, which had two slide switches, and the start/stop one was broken alone with that part of plastic laminate plate that held them. I made a new plate from a piece of Aluminium and moved the forward/reverse switch to the start/stop position and fitted a NVR stop/start in the other position. (see below)

Regards Nick.

[DiogenesIIParticipant @diogenesii]

Jamie, hope it goes well.

Nick – interesting – I've never seen one with those slide switches – they have quite a "Soviet" look to them..

regards both D

[Howard LewisParticipant @howardlewis46836]

If the flange has been removed and replaced, it may be worth just giving it a very light skim to clean it up, to ensure that the chuck sits on a face that is truly square to the axis.

Have you tried clocking it, to check that it is correct in both planes?

Howard

[jamie creightonParticipant @jamiecreighton58639]

thanks,i re check that as well,in the meantime i made a couple of spanners to do the bearing lock nuts up with properly

[Howard LewisParticipant @howardlewis46836]

Ah! That's a good starting point! Another possible source of error to be eliminated.

Recently the locknuts came loose on my mini lathe. Although it wasn't one of his, Ketan spent some time explaining to me, the correct procedure to reset the preload. Following his instructions was time well spent.

Little by little you will fix the various possible causes, until it all comes right.

Don't give up!

Howard

[jamie creightonParticipant @jamiecreighton58639]

would you care to share the instruction please?

[DiogenesIIParticipant @diogenesii]

Unplug the machine and remove the collar, pulley, gear, and key.

Loosen the rear locking ring and snug the front ring up until play is eliminated at the front bearing – the bearings should not be under load and the spindle should rotate smoothly.

A bar in the spindle/chuck to act as a lever will enable you to check more easily for sideways movement.

Having achieved this, hold the front ring still with the spanner and tighten the rear ring to lock it – it may take a few goes to get it feeling just right – patience is the key!

Replace the key, gear, pulley etc. and test run the machine – it should run smoothly and freely at 2000 rpm, and without getting hot at the bearings (warm after prolonged running is okay).

If it feels stiff, "notchy," or labouring to reach maximum speed, you will have to go back, loosen the rings, and release the bearing load by tapping the back of the spindle towards the tailstock with something soft, such as a piece of wood. Repeat adjustment until satisfied – it sounds laborious, but doesn't take long and is worth doing carefully because the improvement in the feel of the cutting action and the finish on the work are marked on this small machine.

The photo's provided by Nick include the section regarding adjustment of the spindle bearings, such as they are..

[jamie creightonParticipant @jamiecreighton58639]

many thanks, basically what i was going to do but thought it best to check from those that have done it.

[Howard LewisParticipant @howardlewis46836]

The method advised by Ketan applies to the mini lathe (Sieg) so may not apply to other makes.

If you want to know what I did, PM me an with an E mail address, and I'll forward it to you.

BUT bear in mind that this is for another make of machine, and so might overload, or be insufficient for another marque.

Howard

[jamie creightonParticipant @jamiecreighton58639]

just an update,

i ran through setting it up again and still no joy.

i then bought new spindle bearings and have just put them in.i will check it all again at the weekend as i also now have a 30mm bit of steel to use as a check for true cutting but on starting it up and letting it run im amazed at how silent it it now is. fingers crossed

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