Project of the Month built by edholly
Home Model Engine Machinist > The Tools and Tips > Machine Modifications > 7 x 12 chinese mini lathe mods

Reply
 
Thread Tools
Old 12-02-2016, 02:54 PM   #1
dkwflight
 
Join Date: Sep 2015
Posts: 28
Liked 10 Times on 8 Posts

Default 7 x 12 chinese mini lathe mods

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


Attached Thumbnails
SAM_0169.jpg  
dkwflight is offline  
Henry Likes This 
Reply With Quote
Old 12-02-2016, 04:56 PM   #2
james_III
HMEM_SUPPORTER.png
 
Join Date: Feb 2014
Posts: 41
Liked 6 Times on 5 Posts
Likes Given: 43

Default

Quote:
Originally Posted by dkwflight View Post
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 donīt have wipers, but I have piece of mudflap rubber under tool, mounted using 2 holes for moving support.


james_III is offline  
 
Reply With Quote
Old 01-05-2017, 09:02 AM   #3
machinedock
 
Join Date: Apr 2016
Posts: 18
Liked 2 Times on 2 Posts

Default

some persons are copying posts from other forums......... like if you also have same problem.
machinedock is offline  
 
Reply With Quote
Old 01-06-2017, 12:21 PM   #4
dkwflight
 
Join Date: Sep 2015
Posts: 28
Liked 10 Times on 8 Posts

Default

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.
Attached Thumbnails
3774-1.480tool holder.jpg  
dkwflight is offline  
 
Reply With Quote
Old 01-06-2017, 05:24 PM   #5
zoltan
 
Join Date: Feb 2013
Posts: 111
Liked 11 Times on 10 Posts
Likes Given: 30

Default

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
zoltan is offline  
 
Reply With Quote
Old 01-07-2017, 03:28 AM   #6
dkwflight
 
Join Date: Sep 2015
Posts: 28
Liked 10 Times on 8 Posts

Default

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 is offline  
 
Reply With Quote
Old 01-07-2017, 03:40 AM   #7
dkwflight
 
Join Date: Sep 2015
Posts: 28
Liked 10 Times on 8 Posts

Default

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.
dkwflight is offline  
 
Reply With Quote
Old 01-07-2017, 10:41 AM   #8
goldstar31
 
Join Date: Feb 2010
Posts: 1,264
Liked 263 Times on 219 Posts
Likes Given: 434

Default

Quote:
Originally Posted by dkwflight View Post
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
goldstar31 is offline  
 
Reply With Quote
Old 01-07-2017, 03:09 PM   #9
Blogwitch
Ex Bogstandard
HMEM_SUPPORTER.png
 
Blogwitch's Avatar
 
Join Date: Dec 2008
Location: Crewe, UK
Posts: 3,385
Liked 591 Times on 445 Posts
Likes Given: 52

Default

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
__________________
If you don't try it, you will never know if you can do it!!
Blogwitch is offline  
 
Reply With Quote
Old 01-07-2017, 06:35 PM   #10
dkwflight
 
Join Date: Sep 2015
Posts: 28
Liked 10 Times on 8 Posts

Default

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"


Attached Thumbnails
SAM_0177.jpg  
dkwflight is offline  
 
Reply With Quote
Reply


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Starting Mini-Lathe Mods cfellows Machine Modifications 81 12-03-2016 01:06 PM
X2 Mini Mill Mods gwapoboy Machine Modifications 27 02-12-2015 03:16 PM
Sieg mini lathes proposed mods bazmak General Engine Discussion 4 05-02-2014 03:06 AM
best mods for 7x10 mini lathe & mill what's yours? sourdoughsmitty Tools 24 04-27-2014 08:22 AM
my mini sX2 mill and mini 7x12 lathe mods (so far!) MCRIPPPer Machine Modifications 14 09-19-2013 03:23 PM



Newest Threads






- Top - Member List