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Tools

Lathe

Necessary?

The short answer: No.

The more nuanced answer is: well, it depends what you are willing to do, invest or otherwise accept. A lathe is not a necessity for kit building or even scratch building. Admittedly there will be some tasks you cannot do but then just don't do them of buy equivalent parts from the market. On the other hand having a lathe greatly enhances your possibilities But please bear in mind it is also more time and money consuming. Learning turning, getting your tools, getting a stock of materials etc. etc. will soon take hold of your precious building resources, both money and timewise.

 

I always wanted a lathe from my early modelling days in my youth. I always dreamed of making my own parts and having those nice shiny things in my hands that I crafted myself. In 2018 the opportunity arose to buy a Unimat 4 from a friend. Of course second hand, Unimat 4s are long out of production but still very sought after. We agreed on a reasonable price that satisfied us both and it landed on my desk somewhere in the summer of 2018.

Motor conversion

I had some startup problems. First the electronics died. After a this relatively small repair the still original motor burnt out. My friend was kind enough to deliver the "after service" of installing a new and more powerful motor which was also capable of continuous running (the Unimat motors were rated for 20-30 minutes continuously). He also added electric speed control for the motor so I could dispense with changing the belts for different speeds.

 

My friend was working in his well-equiped shop...

...on adapting an existing motor to the needs of the Unimat

And in my home my Unimat was awaiting a new heart.

 

...which it soon became

From that moment I was a happy user of this small lathe. I learned to handle the various metals, speeds and tools. I won't claim (anno 2020) that I am proficient in turning but I am getting better results every day and the work become ever more predictable.

Of course I did some tweaking since then, most of it buying additional tooling.

 

Quick Change Tool Post (QCTP)

In May 2020 my QCTP arrived. A QCTP allows you, as you can suspect, to quickly remove and install tools. But the individual toolholders also allow you to adjust the height of the tool which is a considerable bonus. Having this QCTP really saved me a lot of non-productive time during the making of the pivots. It already "paid" itself back!

 

Original EMCO tools are quite expensive and clearly overrated.

I bought my QCTP from Chronos Engineering Supplies. I used their Special Offer which comprised the standard QCTP and two tool holders (May 2020 at £35.94) and which also included another six additional tool holders (May 2020 £8.87 each), on offer for just £58.80 incl VAT (so saving me about £30 on the total of £89.16). The toolpost itself is well made. The

individual toolholders are a bit crude but they do the job well. The order went quick and delivery time was good considering the corona crisis and the consequent delays in mail orders.

The QCTP works extremely well. It is a quick job to install it on the lathe carriage. Installing the individual tool holders is a matter of seconds. If have changed the allen cap head screws for thumbs screw so I do not need an allen key to secure the tool holders. The dove tail mounting secures the tools good enough with the thumb screw. The height adjustment is fabulous, no more fumbling with shims, the tool sits at the correct height every time. The only setback is that the height adjustment can not be locked.

Verdict: a no-brainer. If you can get one, get it.

Toolholder holder

I soon found that my eight toolholders were lying all over the place. So I made myself this little toolholder holder of two layers of plywood. Easy to make, the tools sit well, you can pick them up all at the same time and they have a fixed place to go.

A quick but not exhaustive price comparison

A QCTP from almost identical design is available from Emco Machine Tools, but then costing a staggering £72.00 for the post plus two tool holders and separate tool holders for £22.80 each which totals £208.80. As far I can judge they are not really different from the ones I bought, but maybe they are finished a little less coarse. It is not possible to judge that from the photo.

 

Thee Emco Shop in Austria seems to go completely wild. They sell original Emco QCTP's of very much the same design costing a fat €116.40 (£104.03 as per 25 May 2020) and separate tool holders will put you back €37.20 (£33.25) each, totalling €339.60 or £303.53. As I cannot get a decent picture of them I can not judge if the quality is so much better than my el cheapo.

So to recap

  QCTP + 2 holders extra holders (each) Total QCTP + 8 holders
Chronos Engineering Supplies £35.94 £8.87 £58.80 (offer)
Emco Machine Tools £72.00 £22.80 £208.80
Emco Shop in Austria £104.03 £33.25 £303.53

 


Grinding the chuck jaws

The chuck had quite a bit of run out. So I decided to grind the jaws. I described that on a separate page in the Modelling Tips section

 

Tooth belt drive

The next major operation was installing an alternative drive. The rubber drive belts had many disadvantages, they

  • snapped occasionally,
  • lay a great strain on the bearings of both the motor as well as the main lathe spindle
  • consumed much of the power of the motor in the transmission
  • needed to be removed from the pulleys after use to prolong their lives, a thing I readily forgot.

I ordered two toothed drive pulleys and a tooth belt from AliExpress in September 2020. I took the opportunity to maximise the gear ratio to 1:4.3 to wring every bit of torque out of this motor.

I can't say goodbye to the old belt drive yet as it is still needed to adapt the large pulley to fit on the main spindle. But this is the last picture of it. Oh well, maybe not. The new tooth-belt drive will be just as removable as the old rubber belt drive. So in a matter of minutes I can revert to the rubber belt drive and vice versa should the occassion arise.
The 65 teeth large gear. The remains of a once sturdy bolt wil be turned (excuse the pun) into a mandrel on which the front of the gear will sit while reworking the backside of the gear.
So there it is, turned to a tight but just shy of a press fit.
The main spindle pulley is glued on the mandrel with epoxy and left there for 12 hours.

Then the boss on the back of the pulley is turned down from 40 mm diameter to 30 mm to clear the two large bolts that hold the motor plate to the lathe. The boss is also reduced in height to give a correct lining up with the small motor pulley at a later stage.

 

Now comes the more difficult operation, at least for me as I have never used a boring bar before.

As supplied the pulley has a 12 mm through-hole.

  • It needs to be widened on the bearing side to 16.70 mm to sleeve over the main spindle (1 on the photo below).
  • On the drive belt side it must be turned to 13 mm and then threaded M14x1 (2 on the photo).
  • In between is another small step where it should be turned to 14 mm to clear a non-threaded end of the main spindle (3).

While boring I did not want to take the pulley out of its setup every time to fit it on the main spindle to see where I was. So I turned a stub of brass to the exact same dimension as the maximum width of the main spindle, 16.70 mm and used that piece of brass as a caliber to check the correct width of the hole in the backside of the main spindle pulley. You can see that caliber sitting on the bearing housing of the lathe.

Think the drawing turned 90 degrees clock-wise

Initially the main spindle pulley came off in exactly the dimensions I had in mind. Although working with a boring bar is literally a stab in the dark, with good calculations and decent counting you can get a pretty accurate hole.

 

So far I had only bored the 16.70 mm hole to the required depth.

Too accurate. The pulley would not slide over the spindle, it was too good a match. So I bored out another sliver, bringing the hole to 16,8 mm an then it would slide on!

 

Then I removed the mandrel by carefully heating it with a blow torch.

To work on the front I could clamp it by its boss on the backside. The hole was widened to 13 mm, boring size for M14x1 threading.

Then the bore was threaded with tail stock as a tap follower.

I returned to working from the backside once more to create the middle step which I had overlooked, but this presented no problems.
I also had to take another sliver off the back to clear the washers under the mounting bolts
But it eventually it all came to gether. I could fit the small pulley without any work whatsoever. They lined out as intended and I could start tuning the belt tension by oving the motor mount plate on its bolts.

And this is the end result: a free running lathe liberated from the strain of the rubber belt system.

Future developments

  • Adding a vertical slide to be able to mill small objects with the lathe. I have it but it does not fit well so needs adaptation
  • I have taper tool but it is a tad too high so I must skim off a bit
  • Add a rotary table as an indexer
  • I have digital read-outs that need to be installed
  • Make a whole new underframe from square steel tube, at the same time adding
    • a chip screen at the back and
    • a chip tray underneath