Eric Clark describes how he fitted a readily available faceplate to a Hobbymat MD65 lathe.
A FACEPLATE FOR “UNCLE GEORGE”
Eric Clark describes how he fitted a readily available faceplate to a Hobbymat MD65 lathe.
George was my lifelong hero, mentor and much-loved Uncle. When he sadly died in 1997 my Aunt Ruth very kindly gave me the Hobbymat MD65 lathe that Uncle George had bought to enjoy during his retirement together with lots of other workshop items. So the lathe was christened Uncle George. I had a plate engraved “Uncle George 1925 – 1997” and attached it to the main bed casting as a lasting memorial to a remarkable man.
The Hobbymat had seen very little use and was complete with all the standard pieces of equipment supplied by CZ Scientific Instruments.
Since owning the lathe I have fitted it with a four-jaw chuck, quick-change tool post, slow speed attachment and revolving handles etc, to increase its versatility. However, I never obtained a faceplate as I already have a 1902 Drummond 3 1/2in. gap bed lathe with a 9in. faceplate, which I have always used for flywheels and angle plate work. The Drummond is still treadle operated and following the advice of the late L C Mason in his excellent book “Using the small lathe” I have never been tempted to motorise it. It is a joy to use - but that is another story.
I decided recently to make a faceplate for the Hobbymat after seeing a potentially suitable one advertised in the Machine Mart catalogue. It was nominally 115mm diameter to fit the small Clarke CL250M lathe. The attraction of this faceplate was the suitable diameter, ready availability and the useful mixture of plain and “T” slots across the face. The faceplate fixing is unlike the register on the Hobbymat so a suitable adapter plate would have to be made.
The Hobbymat has a chuck flange semi-permanently attached to the spindle nose which acts as the chuck register plate, see photo 1. It is possible to remove this register plate and fit the Clarke faceplate to it using a quite small adapter. This would reduce overhang to the minimum but would make it very difficult to use the plain fixing slots due to the closeness of the headstock structure.
I believe that some after-market faceplates used to be fitted this way. Also as both my three jaw and four jaw chucks have been fitted to the register plate I had no desire to disturb it every time the faceplate was fitted.
Plenty of access
The adapter described enables the faceplate to be fitted in the same manner as the chucks allowing plenty of access to the rear of the faceplate for fitting nuts and washers and keeps the overhang a bit shorter than that for the three-jaw chuck. Due to the lack of a bed gap and the small diameter of the faceplate only small and light items can be machined so overhang is not too much of a problem. It is however very useful to be able to cope with strange shaped castings that will not go in a chuck. This little faceplate is so nicely and accurately made that I am sure it could usefully be adapted to fit other small lathes that may be out of production. I will describe how I made my adapter together with some guidance notes for anyone who wishes to make one of their own.
Adaptor design considerations
Photo 2 shows the very neat faceplate and the four “T” nuts supplied with it. Also supplied are four x M5 cap head screws to match the “T” nuts and three x M4 centre fixing screws. I had in stock a 4in. diameter part machined chuck back plate that could be made into the adapter.
I did not produce any drawings before I started as the two “business ends” of the adapter were machined to exactly fit the lathe register and the faceplate recess respectively. The usual precautions were taken to ensure concentricity etc.
Fig 1 (above) is a drawing that I produced after the adapter had been made and the design proven. This may sound like working backwards but it is the way many one offs and prototypes are made.
The dimensions given were taken from my particular lathe so if you wish to follow my adapter design please take your own measurements from your particular machine.
The register end
The small end of the casting was gripped in the three-jaw chuck of the Drummond lathe and the outside diameter was machined to 83.5 mm diameter. At the same setting the register was bored to suit the lathe, my lathe = 55.8mm. (Photo 3).
For the final few thous I took the chuck together with the undisturbed casting off the Drummond and offered the casting up to the Hobbymat register until a nice snug fit was obtained. It is of course possible to do this part of the job on the Hobbymat but it is much easier to remove and replace the screw mounted Drummond chuck than the three stud Hobbymat one. Take your time with the last few fine cuts. It may seem the right diameter will never be obtained and then suddenly the casting will go onto the register. At this stage there is still plenty of meat left on the casting for another go if you bore too large and make a loose fit. Aim to get it right first time if you can.
Make the bored recess a bit deeper than the lathe register to ensure the machined casting sits on the correct part of the register. I made mine 3mm deep. I then reversed the casting in the Drummond chuck and rough turned the faceplate end and removed most of the unwanted metal. Make sure you leave the faceplate end about 1mm over diameter at this stage.
The fixing holes
Once the correct fit had been obtained and the waste removed the casting was removed from the lathe chuck and transferred to the Taylor Hobson rotary table set up on my Tom Senior “E” mill to have the fixing holes drilled and tapped. I calculated the PCD on the lathe register from the distance between the holes and using some schoolboy trigonometry found it to be 66mm. (Check yours!)
I found the position of the first hole using a “wobbler” on the O/D of the casting and then moving the mill table along the correct radial distance. In my case this was 83.5mm – 66mm = 17.5mm divided by two = 8.75mm then add half the wobbler diameter. Drill the first hole 5.1mm, which is the M6 tapping size for cast iron. Tap the hole (hand power only) then turn the rotary table through 120deg. Drill and tap the second hole and repeat for the third hole, photo 4.
The faceplate end
Debur the holes and fit M6 x 25mm grub screws or you can use studding at a pinch. Secure them at a depth of 8mm with Loctite. Once the Loctite has set mount the clean casting on the Hobbymat in the same manner as the chucks. At this stage mark the periphery of the adapter to match the reference mark on the lathe register, as this will enable it to be always fitted in the same location. The small “0” marks I made can be seen in Photo 6.
The adaptor is now ready for final turning. First reduce it to the optimum length, about 33mm in my case, and remove any remaining excess metal to give a flange thickness of about 10mm and bore through 16mm diameter. (Photo 5) The object is to make the adapter as light as possible consistent with retaining maximum stiffness. Measure the internal diameter of the faceplate recess as accurately as possible as a guide to final machining. It is tricky measuring shallow large diameter recesses as the ubiquitous digital calliper will always have an error when used in this mode and telescope gauges are too big. Carefully machine the faceplate register to obtain a snug fit ensuring it is deep enough and has an accurate face.
Fitting the faceplate
The final stage is to take the adapter off the lathe, clean everything and fit the faceplate to it. Spot through the three faceplate fixing holes then drill 3.40 mm and tap them M4 on the mill. Clean off the swarf and finally fit the faceplate to the adapter.
Checking for true running
The complete assembly can now be mounted on the lathe and checked using a DTI. (Photo 6) I was fully prepared to have to skim the faceplate to ensure accuracy but to my delight the maximum run-out of the front face was 0.0005in. This was quite remarkable and a credit to the Chinese factory that made the faceplate. The run-out on the O/D was about 0.005in. but this is not a critical dimension so I left well alone.
The final overhang length from the register to the front face of the faceplate turned out to be 40mm, rather less than either of my chucks. This left a 15mm gap behind the rear of the faceplate to enable M6 nuts and washers to be used in the open slots.
The project did not take very long. It was a nice Saturday morning job. Take care to measure your lathe and faceplate castings as accurately as possible. Make the final fit by trying the parts after each very small cut. Try to machine as much as possible at each setting. This ensures concentricity of the mating components. The final faceplate register is turned with the adapter fitted correctly on the Hobbymat. The PCD of the adapter fixing holes should be set as accurately as possible. The fixing holes on my lathe were about 6.8mm diameter giving a sloppy fit around each individual stud. A small error in one location can produce problems when three locations have to line up simultaneously. The studs must not bind in any of the holes as this could cause inaccuracy. I am very pleased with the end result and I am sure that Uncle George would approve.
Resource: Machine Mart Faceplate: order code 060720741 price is about £23. This item is probably available from other importers of the CL250M type lathe at similar prices. A part machined chuck back plate nominally four inches in diameter is available from advertisers in Model Engineers’ Workshop.