I'm surprised by the mini lathe, it has space for large work pieces but is restricted by the travel of the cross slide. I've got a 105mm alu cylinder in there now to make a prop shaft adaptor, it fits fine but the cross slide won't reach the outside of the workpiece to machine it.

I've extended the cross slide knob housing by 20mm and I can just about machine my 105mm work piece now. But now the cross slide travel in the other direction has decreased and caused issues when trying to machine close to the workpiece centre.

I think I need an extended cross slide screw. Am I right that none are available commercially? My lathe skills are pretty basic, I mainly use my machine for making spacers for car projects. Making a screw would be a challenge for me.

I'm still hoping to find a stock lead screw with a thread already cut that allows me to just machine the end that goes into the knob housing.

Can you not get a bit creative with the tool holding? The spec on the mini lathe seems to imply a 70mm cross slide travel as standard so 105mm dia should be within its capabilities.

To face the 105 mm diameter, turn the tool post round and fit a left hand knife tool facing towards the work. the same setup should machine the outside, although you will be limited in the longitudinal travel by the toolpost fouling the end of the cylinder

I tend to agree with Peter Cook 6.

It's surprising what a bit of lateral thinking with tools and orientation can achieve. Modifiying as you are may prove a challenge in the end and more effort than its worth.

You also need to work within the limits of the machine design. The fact that you can apparently fit a piece of work in the available space may prove detrimental to machine performance in the long term if it is stressing motors / bearings etc. We all occasionaly have to push limits, but usually for a one-off job. If you intend doing many larger peces of work regularly in the future I would seriously consider a bigger lathe. I know its ££££ , but this isn't always a cheap ' hobby ' I'm afraid.

Regards Mike

Same issue arises with some industrial lathes. As above be creative with the tool positioning:

Andrew

I wonder how much of the cross slide gib is actually doing anything with that 20mm extension block? Not a good situation, I suspect.

As previous posts, some lateral thinking re tool selection/mounting would likely have been a better solution to that block.

As regards the feed screw, I expect it is a metric trapezoidal thread. Lengths are readily available on the ‘net. The current thread would be removed and a longer length grafted to the remaining feed screw part. That might need some lateral thinking to achieve such an alteration, of course.🙂 Alternatively, making a complete replacement feed screw is an option….

Don't forget that IF you decide to fit / make a longer feedscrew, the thread will be Leaft Hand..

As already said, mountingttb the tooling on the outer face of the 4 way toolpost will increase the diametr capacity.

But be aware that of the power of the machine.. Increasing the diameter of the workpiece means that the cutting forces require a matching increase of torque, which might overtax the motor and / or driveline.

Because of the larger diameter, for the same surface speed, the spindle speed, and motor speed will be reduced.

The lower motor, and cooling fan, speed will mean less flow of cooling air for the motor, so overheating / failure becolmes a possibility!

In the words of a very old radio programme

"Don't force it Phoebe"!

Howard (Wireless keyboard sometimes cam't cope with my low typinbg speeds )

Edited By Howard Lewis on 02/05/2023 14:51:56

Edited By Howard Lewis on 02/05/2023 14:52:30

Philip, I think you will find that the thread is 10 x 1mm pitch with a lefthand thread.

The Little Machine Shop in the USA have them:

Feed Screw, Cross Slide Extended Travel

1 inch longer that is used with their extended travel kit.

https://littlemachineshop.com/products/product_view.php?ProductID=4452&category=

If you can't single point thread it yourself you can find 10x1mm lefthand dies from china via ebay

good luck

Paul

Same as Andrew, I can turn 5" on a 5" lathe only by using a boring bar on the outside.

You will put a large amount of leverage on the carriage.

Don't forget that budget Mini Lathe control boards are not tolerant of overloads

If you do decide to go the modification route, this one is good - I did it to my lathe.

Link

There are several different descriptions online.

As above, you can buy longer screws for the job, but I turned my own (on the same lathe before I modified it) - not difficult with a little care. I have also seen one with an extension pegged and brazed to the original.

Edited By An Other on 02/05/2023 16:55:05

Thanks for the tips.

There's still plenty of engagement on the dovetails (110mm min). I'm only machining soft metal in the large size.

I did see the extended screw sold by Little Machine Shop but I instantly assumed it must be imperial. Now I think about it there may only be one version? Mine is a Sieg SC2 Mini Lathe, metric.

You should be able to buy a length of threaded rod of the matching diameter and pitch and machine the end for the handle to turn it into a feed-screw. Most likely it is a trapezoidal thread (metric Acme, sort of.) Although some hobby lathes have used a standard 60 degree thread. May be left hand thread, depending on your lathe. Plenty of such threaded rod for sale on the net. Sometimes listed as leadscrew etc.

Philip, you could:

Check the screw with a thread gauge, if you don't have any thread gauges use a standard M6 bolt as a gauge they have 1mm 60 degree pitch thread.
Does the hand wheel have 40 divisions, if yes its for a 1mm pitch screw.
Dose the cross slide move 1mm when you turn the handwheel 1 revolution.
When you turn the handwheel clock wise does the toolpost move towards the chuck, if yes its a lefthand thread.

There are 20 tpi feed screws with 50 divisions on handwheel for imperial lathes.