| 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. |
| 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. |
| 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. (Click on image to zoom in) |
 |
Not yet mounted but showing
function. (Click on image to zoom in) |
| 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. |
| 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. |
| 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. |
