Mini Lathe

[David Watson 3Participant @davidwatson3]

I inherited my late fathers Mini Lathe bought by him from Warco in 2005 and it has served me well within its limits for my model engineering projects until recently.

Whilst taking a 10thou cut in mild steel the motor stalled and made some strange noises. I tried a new insert and different speeds but the only way to overcome this problem was to engage the lower speed.

Thinking this could a problem with the brushes I contacted Warco to confirm they stock the brushes. Has any one had this problem and can confirm my thoughts.

[David Watson 3Participant @davidwatson3]

Motor Problems

[David George 1Participant @davidgeorge1]

I wonder if there is a problem with the gearbox or drive system. With the power off try and rotate the chuck by hand and see if it drives the motor. Then change the gear to other ratio and try again, will the motor turn in this as well.

David

[David Watson 3Participant @davidwatson3]

Thanks for the thoughts Dave. I am sure the problem is not mechanical because it managed the same cut in the lower gear.
The noises were not mechanical. Thinking about this it was a buzzing noise from low down at the back were the motor is. I have since found a picture of the motor and it looks like one of the brushes is fairly easy to get at so I might check that next.

[samuel heywoodParticipant @samuelheywood23031]

Hello David, sounds like you have a "Real Bull" manufactured mini lathe? A version of which i have also have.

If so, i've always found it easy to stall in high gear & yes it does make some strange noises when that happens~ doesn't seem to have a trip out~ i hit the stop button as quickly as possible.

From your post it sounds as if you are quite conversant with it's capabilities & a 10 thou cut in "Hi" normally works for you?

DOC does rather depend on work diameter? which you haven't stated~ i'd expect a stall likely on a 10 thou cut in steel in low gear if i was turning 4" to 5" dia steel.

I Hope that isn' too much teaching grandpa to suck eggs.

I would check out Davids suggestion, if only to eliminate it from your enquirys. You can chip a gear tooth off & it runs perfectly fine in one gear & 'seems' to run in the other.

Both motor brushes should be easily acessible once you remove the motor cover~ disconnect the power first

( ask me how i know!) so you can then compare the length/condition with the 'new' spec.

Wouldn't hurt to clean up the stator with some alcohol dipped cotton buds while your at it to remove any excess accumulated carbon dust.

[David Watson 3Participant @davidwatson3]

Thanks for youre thoughts Samuel,

I try and be careful about the material I use for my projects considering the limits of the mini lathe. The lathes I have worked with in the past had varied from a Harrison, Boxford and an ML4 Myford. They all had there limits of cut but unknown materials were always going to be an issue.

This time I was reducing a 1" shank on a MT2 arbor to thread it 5/16 x 32 to use in the tailstock. The tool I was using was a new one with a diamond shaped insert. I swapped back to my normal tool yesterday and it seemed to help.

I tried another MT2 arbor with the same results but turning the same size free cutting mild steel didnt cause any problems using the new tool and insert. Maybe I was too trusting thinking the arbors would turn as per mild steel.

Once the current project is finished I am going to move the lathe and look into this problem further. I need to get to the back of the saddle at the same time to sort out another issue I inherited. Why do problems always come mid way through a project.

[Howard LewisParticipant @howardlewis46836]

"Diamond shaped insert"? Carbide?

I cut MT arbors quite satisfactorily with a diamond shaped tool, but it is HSS, (Eccentric Engineering or home made tangential tools )

Moulded carbide tips ar not sharp; a ground Carbidetip or HSS tool are!

Tools are always set to centre height with a gauge.

Just my experiences (And I do use moulded carbode tips for roughing, boring or radius turning, satisfactorily enough for me. )

Howard

[David Watson 3Participant @davidwatson3]

It is DCMT 07 carbide insert that came with the tool. I bought it to machine a relief for threads against a face. In that respect it works well but maybe for longer cuts I will stick to my normal turning tool.
If the quick change tool post comes to being I have more chance of getting the tool on centre hight without resorting to shims.

The tools that came with the lathe are a mix of 6 &8 mm all with carbide replaceable inserts. I also have some of my own carbide insert tools and odd tool steel home ground tools. With this mix setting them on centre hight is always a challenge.

[David Watson 3Participant @davidwatson3]

A quick update regarding the motor problems. I took the rear brush out of the motor and there is a lot material left on it so I didnt take the other one out being harder to get at. As suggested I cleaned the stator whilst the brush was out.

As part of my next project I have been cleaning up some 2" round bar. I didnt try in the high gear and used my origional turning tool with no trouble. This must prove it must have been the arbor I was turning down must have been some odd material.or the wrong tool for the job.

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