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The SQ Engineering Lathe

Initially there was no plan for a lathe in the workshop. It may be a strange statement for a business such as this but off site facilities where available once a week. However the need for the regular access for machined parts become enough to justify the purchase of a second hand machine.

Lathe purchase and repair:

After a search over an extended period of time a potentially suitable lathe was found on ebay. It was an old Australian made Hercus model. On inspection it had huge slop in the cross feed and some in the slide. Taking the chance the bid was won for the starting price. It came with an aftermarket 125mm (5") 3 jaw chuck that had already been adapted, a non independent four jaw chuck (very unusual!) and a few other bits and pieces. It was powered by a 370W (1/2HP) three phase motor with some cut off wiring.

Taking the slide apart, it didn't take long to find the two main issues; a worn out cross slide nut made from sintered bronze and a worn down travel wheel (X axis) shaft. To some surprise brand new parts could still be sourced from the original company Hercus. Also discovered from calling Hercus was that the lathe was made between 1952 and 54! A new cross-feed nut was ordered and later a dedicated tool post spanner. The slide wheel shaft was a different story, the original design unusually had no bushing between the shaft and the cast housing, only one of the many intricate oiler points. So with some extensive setting up the housing of the carriage itself was machined reamed out to exactly 20mm and the shaft was machined down to 14mm. A sintered bronze bushing was pressed into either end of the housing and then re-assembled. The final result was still some slop from the gears them self but still significantly less than before.

A new single phase 750W (1HP) motor was fitted with the amazing ease of two extra drilled holes with the old pulley swapped over. A new belt for the motor was also fitted and a universal belt for the gearing change pulleys. A universal length V-belt was used for the gearing pulleys because if a conventional A-type belt was fitted then the whole head assembly would of had to be taken apart.

Also purchased was a set of new (non genuine) change gears to allow for more range in thread cutting.

Carriage stripped down, chuck removed, new single phase motor bolted into place and the new universal V-belt fitted.

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Closer look at the disassembled carriage. On the left hand bottom the custom plate is visible that adapts the larger non standard three  jaw chuck. The red drawn arrow in the bottom middle points at the slide wheel shaft hole that needed to be machined out for the fitment of two bronze bushes.

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A closer look at the gearing change system. the lever in the back takes the tension off the belts for gearing changes.

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Messy wiring! The start stop station was taken off with the plate behind it and all the wiring removed. Later a brass knurled knob will replace the missing one off the switch and it will switch single phase power instead. An emergency stop near the operators knee will also be added incline for safety.

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Reassembled and ready for more work! Wiring still needs doing, the tail-stock needs to be adjusted for alignment more accurately but otherwise it works surprisingly well.

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Crude DRO Upgrade:

Seeing the readily available DRO's available that looked like the same technology as digital verniers I thought I would try one. Although I felt very uncomfortable drilling into the machine itself for the mounting it had to be done.

After making a crude bracket and some extensive testing I concluded that it worked much better than I expected. However even though I offset the scale quite far backwards it still meant I had 20mm less room to move the tail-stock in, an even further offset bracket would achieve this. I also found that that the lead out of the scale was always quite loose and with a bump it would fall out, so with a simple loop and a bit of hot melt glue my problem was solved for good.

So for the tiny cost of one of these units I highly recommend them, they work great, the screens are good and they have a 0.01mm resolution

Scale mounted ready for use.

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Not yet mounted but showing function.

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Lathe Grinder Upgrade:

Due to the need to machine some 4130 Cro-Mo shafts that didn't typically leave a nice finish when turned down with my normal tungsten cutters I needed a new approach. So in a flash of creative thinking I adapted a 150mm (6") grinder to my cross slide. Using a quite simple means it bolted to the existing fixture.

The result was quite good and was easy to use, I faced the motor to rotate upwards at the contact face to counteract the lathe spindles direction. In the future when a reversible motor is available on the lathe I would change it to face it down. The most comical part of this conversion is that it cost me in total under $15 dollars including the grinder!

I have since been warned however that the dust coming off the grinder wheel has a severe effect on the lathe slides because of it's highly abrasive nature. So I just keep the slides covered when doing grinding and have a very good clean when done.

Clamped down with fixture ready for use.

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Grinding in action on some 4130 Cro-Mo pipe.

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Surface finish on 4130 Cro-Mo pipe. Finish could be improved further with a finer grit stone, running wet and also balancing the stone better in the grinder.

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Lathe In Use:

This video is taken from my scooter build and it shows this lathe in use through a time lapse video. Although not shown in the video is the removal of the hub from which it was machined further in a dividing head on a milling machine. It was on this mill that the spoke holes where drilled, disk brake mounts drilled and tapped and reliefs cut.

Professional Digital Readout Upgrade:

In the normal use of my crude yet effective digital scale I found it would jump in 0.02 to 0.03 increments. Thinking it was the cross-slide being sticky I took it apart for a clean and re-grease. Putting it back together I found that it made no difference. Out of frustration I considered changing to a DRO with a higher resolution. The online company M-tech where offering SINPO branded kits on ebay  (Username: Thethedrostore) with the optional extra of a 0.001mm resolution which was 10 times greater resolution than before.  I was apprehensive about going for model of DRO that was sold online however I decided to take a chance due to the very helpful support from the company, the excellent easy to read documentation and in a worse case scenario the scales and screen where directly interchangeable with the common locally used DRO's. Upon ordering it took only a few days before a courier dropped off the relevant boxes to my workshop.

I ordered the kit which included the main screen, two slides and a very comprehensive selection of assorted pieces to mount everything such as brackets, shims, cable ties and clips. SO as to not have any accuracy issues I decided to use some very solid mounts, 10mm thick for the bracket that held the main scale and 8mm thick for the digital readout slider. It took about 3 days start to finish to do the job as I spend a considerable amount of time lining up the scales.

The scales had an automatic radius/diameter compensation built into it, this is used because when a lathe tip takes 1mm off a piece of round it gets taken off all round and hence seeing that 1mm is taken off both sides 2mm gets removed overall. Previously I had to halve all my measurements with a calculator to work out where I needed to end up at, now with this system I take a light cut, measure it, input it into the DRO and then I just keep cutting till I get close to where I want it. Because of this compensation the scale moves in 0.002mm increments instead of 0.001mm.

In testing I unwittingly discovered my previous problem of the jumpy readings; it was the old scale itself, or rather the thin metal mounting it had. The reading I was seeing was the scale holding in one position with the friction until the springiness of the bracket was taken up which would then cause it jump forward 0.03mm. With the new scale I could easily move forward the minimum 0.002mm at a time with ease. Setting the scale on a known diameter I found it was fantastic in always knowing exactly where I was and a was a real pleasure to use.

The only real downside is that the contrast on the screen is poor, in full light it's just not possible to read the screen at all. I will install a shroud around the screen in due time but for now I am fine as I usually use my lathe at night time, otherwise so far it's been a great unit.

The official photo of what the kit is supplied with.

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The DRO installed and ready for use. I did make a longer screen mounting bracket to suit the machine though.

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The custom bracket that holds the scale, originally a 20 x 10mm solid bar but chopped length ways to all for the maximum amount of tail-stock movement. Shims where installed under one end to have the correct level.

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This 25 x 8mm bar is attached to the bottom of the cross-slide and holds the scales reader head. I purposefully chose an extra long scale so that I may install it on a different larger machine in the future. Only a small part of the dust cover could be used.

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The main slide scale shown with the dust cover installed.  This scale is held in a very well protected position as it faces down and well inside the cover. The covers, clamps and most of the fasteners where all supplied with the kit.

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The mounting of the reader head of the main slide. It is attached to the cross-slide carriage where a steady would normally be bolted up. The cross-slide scale mounting is also visible. Again the brackets clips and ties where all supplied.

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As always questions and feedback are welcome: