Busy Bee/ Craftex 7 x 12 Lathe

[gwapoboy]

Hey everybody, I am still pretty new here but trying to get more involved. Just a bit about me, I am an apprentice Tool and Die Maker, have been machining for a decent amount of time. Anyways Today I picked up a 7 x 12 Mini lathe from my local busy bee tools. I had a 7 x 8 but found it a bit to small for my needs, So I sold it. However I kept the extra metal change gears it came with when I sold it thinking they may come in handy with the 7 x 12.
One Thing I will say is for the price you get ALOT compared to what Ive seen most other mini lathes come with. I got it for $729.00 Canadian Plus 13% Tax. Comes with change gears ofcourse(not sure if they are plastic or metal havent checked yet guessing plastic), Steady rest, solid mt2 Center and Live MT2 center, Face plate, extra fuses, a couple chip guards, SPRING LOADED chuck key(Really impressed by this as its a nice safety feature). And a few other things. One thing though I did notice is on there website it says it has a 1/2HP motor, but according the the manual and label on the front of the lathe its a 300W motor which is .4HP if i am not mistaken.

Anyways, I am planning on putting a 4" 3 Jaw chuck on it(got the backplate adapter arriving today hopefully). I do want to convert it to CNC Eventually so I was wondering if you guys know of there I can a kit of atleast the Ball Screw kit with motor mounts.
Next thing was Upgrading the Spindle Bearings is it worth it and how much of a difference can it make? If i was to upgrade the spindle bearings would a 1 ton arbor press be big enough/heave enough force to do it?
Lastly if there any other upgrades you guys suggest to improve the accuracy/performance of the lathe?

Thank you very much for you time/replies in advance

Justin

 

[canadianhorsepower]

welcome here are some usefull links
http://www.machinistblog.com/free-plans-ball-turning-tool-post-for-the-7x-mini-lathe/
https://www.buildyourcnc.com/electronicscombo.aspx
http://www.micro-machine-shop.com/

http://www.hobbycnc.com/products/hobbycnc-ez-driver-board-combo/

enjoy

 

[Brian40]

Hi and welcome , if it will help take a look at my site (see bottom of page) it covers most of the things you need and how to do it, just down load the PDF's it's free,how's that for a deal.
Best Regards Brian.

 

[Theclockworks]

Hello and welcome regarding bearing change you may like to look a this guide.

http://www.arceurotrade.co.uk/machineguides/C3-Mini-Lathe-Dismantling-and-Reassembly-Guide.pdf

 

[gwapoboy]

Thanks for the reply's Everybody. One thing I was wondering is I got a backplate to put a 4 inch 3 jaw on, will doing this possibly increase any runout the machine has?

 

[///]

It can yes, it all depends on how accurately the backplate registers were machined.
What I typically do when I get a new lathe is lightly punch a reference mark on the outside of the lathe spindle, then I mount the chuck and measure the runout, noting the chucks orientation and writing this info down, I then undo the chuck bolts/nuts and rotate the chuck to the next group of holes(120 degrees for a 3 jaw, 90degrees for 4 jaw) on the spindle and repeat the measurements. I do this a few times round to triple check my measurements.
Once I find the location with the least runout, I then lightly punch a reference mark on the chuck that lines up with the mark on the spindle.
This means when I remove the chuck, I can replace it to the location with least runout quickly.
With a backplate this gets done twice. Once thru for the backplate to spindle, then when the least runout is determined for that pairing, do it again for chuck to backplate.
Hope the above makes sense.
I have some pictures of my reference marks but not on my phone, will update later.

It can take some time to do, but it is ultimately worth the effort.
For example, I recently did this for my ER32 collet chuck and backplate, fitted randomly I measured the backplate register runout of 0.05mm (0.002"). With the Collet Chuck fitted randomly it blew out a further 0.03mm (0.0012") to 0.08mm (0.003"). These were fitted randomly, so it is possible that located in different orientations it could have been worse!
After going thru the above process, I found the backplate's least runout of slightly over 0.01mm (0.0004") and with collet chuck fitted in it's best location, a total (backplate and chuck) runout of 0.03mm (0.0012"), measured inside the collet chuck's tapered bore, these measurements were repeatable.

 

[Cogsy]

I recently did this for my ER32 collet chuck and backplate

I'm just thinking aloud here, but is it possible that some of the runout could cancel itself out if you tried other combinations? I'm thinking along the lines of maybe one backplate orientation has say 2.5 thou runout, but one position of the collet chuck may have 3 thou runout in exactly the opposite direction. I'm thinking the total runout would then be half a thou.

If runout does cancel out like that then maybe it's worth checking other backplate positions rather than just the one with the least runout? Just something I was pondering so I thought I'd post it.

 

[///]

Yes, I reckon it is definitely possible.
I thought of this too, but only after I had spent the time doing the above procedure and stamping the reference marks! Typical.
It was around 2 or 3am at the time so poor brain wasn't exactly running on full steam.

I do plan to go back and try this, also noting which direction the runout is moving on each orientation rather than just the amount of runout for each orientation.

I also need to try locating my chuck when the backplate is nice and hot...... reason for this.. I had machined the 72mm chuck register on the backplate after a lot of facing cuts.
The chuck felt nice and positive against the new register and I then went to remove the backplate from the spindle so I could bolt the backplate to the chuck.
I noticed the backplate was very hot to the touch(I don't have a coolant system yet) and I immediately thought about shrinkage.
Sure enough, once the backplate had cooled, the register was noticeably loose against the chuck. Drat.

Lesson learned, wait for the work to cool after lots of roughing cuts before making cuts to size!!

My theory however is that I might be able to heat up the backplate in the oven so the register is tight again, then bolt on the chuck, let cool and check to see if the runout has improved.... will it work? no idea, I hope so, it would be nice to get runout down to half a thou or even less.

 

[DJP]

The problem with excessively chasing run out reduction is that machines get old and worn. My 1940s Southbend and a worn out 3 jaw chuck taught me this lesson. Even if you can improve run out a little the problem will be back. A new chuck and a freshly machined back plate is as close as this machine will ever get to minimum runout. I deal with it by keeping a part chucked for as many operations as possible and marking it if it needs to be removed from the lathe so that it can go back to the same jaw positioning.

As much as it would be nice to have a new tight lathe, I dearly love the old Southbend for the work that it can still do. It's a keeper.

 

[gwapoboy]

Checked the run out of the stock 3 jaw with a precision bar thats machined to 0.0002 runout max. and found the best I could get the runout to was 0.009 which doesnt seem right atall any ideas?

 

[canadianhorsepower]

It is high
semove your chuck and check your adapter plate
to see how straight is it

 

[gwapoboy]

It is high
semove your chuck and check your adapter plate
to see how straight is it

I checked and the runout was 0.0005" but I didnt check if it was square or not ill check that for sure. Was really wierd as i thught they should be 0.003 at max run out with the stock 3" 3 jaw

 

[canadianhorsepower]

I checked and the runout was 0.0005" but I didnt check if it was square or not ill check that for sure. Was really wierd as i thught they should be 0.003 at max run out with the stock 3" 3 jaw

but always keep in mind that a 3 jaw chuck is not the most
precise things ever :fan:

 

[DJP]

I fussed with better precision from an older 3 jaw check and even though I could get min runout at one diameter of work piece the chuck was out again at a different diameter. I think that it is the nature of the beast to be fast and convenient but not that precise. On my chuck I concluded that the scroll was worn or it was not right from new. 3 jaw chucks are not expensive which also means that they are not built to tight tolerances.

I would not expect too much from a 3 jaw.

 

[gwapoboy]

an very quick measurement showed the backplate was withi 0.002" going to take some more time tomorrow to measure it and a few other things with my Dial Test indicator as its more accurate the the indicator I used today. one thing I was wondering is would taking the 3 jaw apart cleaninging it and lubricating it properly possible help with the run out?

 

[canadianhorsepower]

I was wondering is would taking the 3 jaw apart cleaninging it and lubricating it properly possible help with the run out?

Nope it would not change anything
the best way to explain the "no precision" in a 3 jaw chuck
is simple compare the thread of your chuck to a regular bolt
and a ball screw

Thats why when you start something with a 3 jaw don't remove it till you are done

cheers

Luc

 

[gwapoboy]

Nope it would not change anything
the best way to explain the "no precision" in a 3 jaw chuck
is simple compare the thread of your chuck to a regular bolt
and a ball screw

Thats why when you start something with a 3 jaw don't remove it till you are done

cheers

Luc

Just finished measuring the back plate more and the bore of the mt3 taper. All the important surfaces are within 0.0004"" at max others where 0.0001" . So with that guessing its fair to say its the 3 jaw chuck? Going to be getting a 4" 3 Jaw chuck anyways so hopefully its got slightly better runout

 

[canadianhorsepower]

Just finished measuring the back plate more and the bore of the mt3 taper. All the important surfaces are within 0.0004"" at max others where 0.0001" . So with that guessing its fair to say its the 3 jaw chuck? Going to be getting a 4" 3 Jaw chuck anyways so hopefully its got slightly better runout

all depending of your machining work but I think you should try a 4jaw
chuck it's longer set up at the bigining but when use to it
everything will be dead on

 

[DJP]

A 3 jaw is just too convenient for everyday tasks to ignore. Just buy a new one and I'll bet it runs better. That was my solution. The 4 jaw sits ready for those special jobs but for 99% of what I do the 3 jaw is perfect. I keep a small centre punch handy and if a work piece needs to be taken out of the 3 jaw chuck and replaced later, I mark it with a punch mark beside jaw #1.

If you are dealing with an old chuck it may have worn jaws as well as a worn scroll. If you clamp the rear portion of the jaws on a socket, you can machine the front portion of the jaws with a carbide boring bar. It helps but only a little.

It's best to just buy a new one.

 

[canadianhorsepower]

A 3 jaw is just too convenient for everyday tasks to ignore.
It's best to just buy a new one.

DJP
be serious on your opinion
you are making people beleive that dial gauge are useless:fan:
do everyone in thi group a small video why would your 3 jaw chuck
equal a 4 jaw chuck:fan::fan:
good luck