By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

hobbymat not cutting Parallel

All Topics | Latest Posts

Search for:  in Thread Title in  
jamie creighton06/01/2020 18:12:37
10 forum posts

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.

Howard Lewis06/01/2020 18:32:52
2699 forum posts
2 photos

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 creighton06/01/2020 19:14:55
10 forum posts

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 Wick06/01/2020 19:42:55
123 forum posts
4 photos

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

JasonB06/01/2020 19:53:18
avatar
Moderator
17020 forum posts
1825 photos
1 articles

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

Oldiron06/01/2020 21:33:26
354 forum posts
22 photos

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 creighton07/01/2020 04:22:38
10 forum posts

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

DiogenesII07/01/2020 06:56:28
56 forum posts
6 photos

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..

Hopper07/01/2020 08:49:28
avatar
3944 forum posts
83 photos
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 Farr07/01/2020 11:18:44
avatar
2064 forum posts
988 photos

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.

m&l1.jpg

m&l2.jpg

m&l3.jpg

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.

DiogenesII07/01/2020 13:30:32
56 forum posts
6 photos

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 creighton07/01/2020 16:48:32
10 forum posts

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

DiogenesII07/01/2020 17:08:36
56 forum posts
6 photos

Thanks for clarifying..

jamie creighton07/01/2020 17:36:50
10 forum posts

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 Farr07/01/2020 18:40:05
avatar
2064 forum posts
988 photos

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)

Switch Plate 2

Regards Nick.

DiogenesII07/01/2020 20:05:38
56 forum posts
6 photos

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 Lewis08/01/2020 20:11:36
2699 forum posts
2 photos

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 creighton09/01/2020 18:08:07
10 forum posts

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 Lewis09/01/2020 18:51:48
2699 forum posts
2 photos

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 creighton09/01/2020 19:14:42
10 forum posts

would you care to share the instruction please?

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Allendale Electronics
Ausee.com.au
cowells
Warco
ChesterUK
emcomachinetools
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest