7 x 12 chinese mini lathe mods

[dkwflight]

Hi
I have had this mini lathe Kit for some time.
I added a 4" 3 jaw chuck.

I up graded the ball bearings on the spindle to better ball bearings. The tapered bearing mod had not happened yet.

I noticed during interrupted cut the tool holder was bobbing up and down.
I added extra gib adjusting screws to the compound. This helped.

I was getting some movement in the carriage still. the original carriage hold down strips were using a poor method of adjusting the clearance. The strips had a narrow wear pattern due to the strips being cocked to the ways, wearing on the bottom outside edge of the ways only.

I heard some where about changing the carriage hold down strips for a heavier strip held with studs. Adjusted with shims. The strips I made are about 5" x 3/4" x 3/8"
THe extra length helped the carriage stiffness. The left end of my new hold down strip hits the motor cover at the far left of travel. I should probably take off 1/8", not a big issue. The 3/8 thickness was too thick, I had to carve a divit where the carriage traverse gear meets the rack under the front way. I also used a stone under the ways especially on the rear bottom of the ways to remove extra blue paint. The serial number on the right end of the way had raised edges, some stone work there took care of that.
This proved to be a much better way of setting the clearance in the carriage to ways. The carriage could now be slid sideways with a couple fingers pressure. The up, down movement now is much less.
I still get some movement during interrupted cuts, much improved.

I bought the metal change gears. also a big improvement.

I installed the lead screw cover recently introduced by LMS.
This mod keeps the lead screw and half nuts much cleaner.
I lost some carriage movement at the right end of travel though.

I bought the extended travel and lowered carriage mods from LMS. Good people there.

Someday I will make way wipers for the carriage.

No original ideas here , all stolen from others

 

[james_III]

I noticed during interrupted cut the tool holder was bobbing up and down.
I added extra gib adjusting screws to the compound. This helped.

This is on my list, I was just waiting if someone had done something more clever. I don´t have wipers, but I have piece of mudflap rubber under tool, mounted using 2 holes for moving support.

 

[machinedock]

some persons are copying posts from other forums......... like if you also have same problem.

 

[dkwflight]

Hi
I have since added the OXA qtcp from LMS.
This tool post seems to be a good investment. The tools are closer to the hold down stud.
It seems to improve the ridgity of the little lathe.
I also like the new boring bar holder. It works well.

With the old cut off tool holders I had a lot of difficulty with the cut offs.
The 0XA for 9x20 Lathe suited me because of the lowered carriage cross slide.
The number 7 parting blade holder holds the parting tool at a positive angle. This improves the cut off operation a lot for me.

I still have an alignment issue with the head stock.
The little lathe is not too great for being ridged or correctly machined to begin with.
More work to be done.
I just checked the head stock run out.
I made a 1" internal diameter bushing for a power hack saw. I ended up with a taper. After checking my test bar, I found no run out.
The issue I now believe was the cheap chinese boring bar. Not enough relief at the cutting tip rubbing causing a taper.
I have run into details of how to grind these boring bars so they will give satisfactory service.

 

[zoltan]

You may want to check my blog for other mini lathe mods to consider. I think especially useful ones for you would be the gib modification, the compound delete, the way protector, and the way wiper.

http://benchtopmachineshop.blogspot.com

 

[dkwflight]

Hi Zoltan
I have done most of the mods mentioned in your blog.
THanks
I shimmed my carriage gibs with the screws changed to studs and lock nuts.
I made replacement gibs from a larger thicker piece of steel. My gibs are about 5/8 longer than the carriage on each side front and back adding more stability.
I had the carriage off recently and noted the wear was very uniform compared to the OEM gib/ adjustable bars which wore only along the outer bed edges in a narrow path.
I made mine of 3/8 thick stock, too thick. The carriage gear needed a divit carved in so the apron could be installed. Installing the apron is still a bit difficult needing the lead screw mount loose on the right side to get the require clearance.

I am very satisfied with this mod.

I bought the milled down carriage slide from LMS. When I examined the old carriage I could see the wear was heavier on each side of the carriage showing the carriage was rocked towards the tail stock from tool pressure ETC.
The new heavy gibs are helping this kind of wear.

I also installed the lead screw cover kit from LMS. Not totally satisfactory. The kit shortens travel to the right. Also the end brackets needed to be swapped to put the mounting tabs above on the end brackets. The directions called for the tabs to be on the bottom putting the mounting screws in a casting hole It does keep the lead screw and half nuts cleaner. I made a cover for the area where the threading dial engaged the lead screw.
I find the threading operation much easier to keep the half nuts engaged all during the threading operation. This limits possible errors from missing the engagement of the half nuts.

 

[dkwflight]

Hi

I looked at several schemes for locking the carriage for facing cuts.
None looked very satisfactory.
I find putting the tumbler/ lead screw in neutral and closing the half nuts. The tool pressure pushes the carriage to the right during facing cuts. The compound slide adjusts the tools for facing cuts.

 

[goldstar31]

Hi

I looked at several schemes for locking the carriage for facing cuts.
None looked very satisfactory.
I find putting the tumbler/ lead screw in neutral and closing the half nuts. The tool pressure pushes the carriage to the right during facing cuts. The compound slide adjusts the tools for facing cuts.

Certainly it is an age old problem but you might get 'compensating tolerances' - if you are lucky. Statistically, I'd rate it along with 'Rocking horse manure'

The old way is to utilise a clamping motion by nipping up the front gib- preferably- until the whole thing becomes solid.

Of course, I'm a heretic. I have pinned gibs and have added at least one additional adjusting gib screw- which is pointed screw rather than a rounded or square one.

Again, I don't add a QCTP to wobble about or a front parting tool.
Laughingly, I was born in a thunderstorm- and have my rear parting tool upside down- at a slant( to avoid loss of height in regrinding) and the upside down kerf- vee'd 140 degrees.

As a very uncouth old geriatric, I looked for the people who actually won cups for their craftsmanship- and - because it seemed a good idea.- copied them

Time to oil my wheelchair?


Norman

 

[Blogwitch]

I restored a mini lathe many moons ago and that required a saddle stop to stop it being pushed away from the chuck when taking cross cuts and this was about the best method that I could come up with and it solved ALL the problems.

Get a bolt of say 8mm and put a small brass insert into the end, this one was a commercial one.

Go to the back of the saddle, nearest the tailstock and mark off a point were it sits half way across the way nearest the front of the lathe and then centre drill, but not too deep.

Disconnect the leadscrew and move the place you want to drill through on the saddle off the back of the ways so you don't drill into the way. Drill right through and tap out for your bolt.

Reassemble everything and put the bolt into the hole just drilled, and if you set it up just right, 1/8 turn will lock the saddle up solid.

Hope this helps

John

 

[dkwflight]

Hi

If my carriage on my Homier/ Speedway looked like yours I certainly would have gone with your method.
As you can see my carriage is not made like yours. I wish it was.
Also you can see the carriage hold down/ adjustment strips stick out about 5/8"

 

[Blogwitch]

The way with yours might be a small toggle clamp like this

http://www.ebay.co.uk/itm/2pcs-101A...ffType=OrderSubTotalOffer&_trksid=p5731.m3795

And instead of having the rubber on the end, turn up a piece of brass instead to fit. They should go down small enough to fit the areas you have.
Or else, bolt a piece of 1/2" bar between the two sides and fit something similar that I showed above, or even recess it into both sides.
It really is worth the effort to do this sort of mod.


John

 

[bazmak]

The method you have used is not the beast for locking the carriage as it lifts the carriage
off the ways.The best method has been described many times with a clamp under
the centre of the way and a central locking arm that pulls the carriage down on to the ways

 

[Blogwitch]

Baz, that is the way of the commercial providers of saddle locks.

Neither way is ideal Baz, people tend to forget that you should have a film of oil approx 0.002" thick on the ways if the correct way oil is used.
Both yours and my way will either expand or compress that oil film, assuming that the gibs have been correctly set up beforehand with that film in position.

Just as a side note, woe betide anyone who doesn't keep their machines well and correctly lubricated, they are heading for throwing away the machines after a few years, worn out by metal to metal contact, forever destined to be adjusting gibs to keep them on track.

John

 

[goldstar31]

Respectfully, I think that the word 'thickness' is missing. Obviously, one cannot compress liquids of any type. Probably, one of those days?

Again, I'm looking at the saddle on my little ML10 which has been left on the bed so that I'm able to single handedly, tote the thing into the 'warm'. Again, I think that you possibly mean 2/10ths of a thous rather than a whopping 0.002"

Or am I heading for the comforting bosom of Matron at the adjacent 'Fruit and Nut farm' conveniently just over from the Goldstar residence?

Cheers

Norman

 

[Blogwitch]

Not 2 tenths Norman, but your whopping 0.002". Of course, if a thinner lube (the wrong one) is used, then of course the film would be a lot thinner. That is why machines should be lubricated very often with the correct grade for the area it is to work in, on my mill, the autolube gets a shot every hour, because as the ways are moved about, oil spills off the edges of the ways and so that film then soon gets to a metal to metal situation. If it was 2 tenths, then that might be every five minutes it would need a shot.

As you say, most 'liquids' are not compressible, but they can be forced to spread a bit more and get squeezed out with a lot more pressure, or in my way, sucked into a thicker pile.

You should know all this Norman as when I was in the services, it was a major issue when servicing and keeping aircraft flying, but then again, my service was most probably a little later than yours and we had such things as hydraulic powered flying controls. Whenever the aircraft landed, lubes were pumped into all sorts of orifices to keep things running smoothly, sometimes as often as every couple of hours on helicopters as there are a lot of centrifugal forces involved. I suppose that is all done automatically nowadays as the aircraft is flying.


John

 

[dennisa49]

Good day,
The bearing manufacturers SKF have an excellent outline and schedule related to bearings - plain, roller, ball - laying out lube requirements.
It is worth a read. They have a system calculator for all bearing requirements and all varying conditions and loads.
It is surprising how little grease is needed to keep a bearing properly maintained.
Like John I did my time on aircraft engines, then later in asphalt production maintenance. Not outlining my CV., just the reason I looked for info.
The info is high quality.
www.skf.com>grease-lubrcation
Hope this adds to the discussion,
Dennis
ps. hydraulic controls were the go

 

[bazmak]

Back on track please boys.We are talking about a simple saddle lock
on a cheap chinese mini bench lathe.All I proposed was a lifting clamp to the underside of the ways,not a clamping screw down on top of the way

 

[zoltan]

I agree with bazmak that a lock which clamps the saddle to the ways is preferable to one which lifts it up from the ways.