Lathe rebuild

October 2013

I wanted a small lathe to turn parts for rockets (esp. exhaust nozzles) and also to use as a mill for small parts – I was fed up with small brackets and things which looked like they had been cut with a blunt chisel. I also needed something I could lift and carry up the stairs into my workroom, which is in the loft.

I plan to convert the lathe to CNC, but retain the manual controls. I have already experimented with CNC with my 3D printer build. I expect that adding CNC will enable me to make complex and curved shapes such as a de Laval exhaust nozzle, as well as make thread cutting easy.

I will focus on the MD65 lathe here and cover the mill in another post. The mill table is VERY heavy and will have to go into my garage. For now I have sprayed it with silicon spray and put a paper bag over its head.

Purchase

I looked at micro-lathes which were around 23kg, including the Seig C1 and the Taig Micro-Lathe 2. The Taig in particular appears to be highly regarded, and is extremely capably for its small size (have a look on youtube for Taig lathe videos). However, I had a niggling doubt about distance between centres – I wanted to turn threads or circlip grooves into aluminium engine casings, which I expected to be about 300mm long – this is out of reach of all of the micro-lathes.

So I looked at mini-lathes which are heavier at around 45kg but more capable, and with enough stiffness to handle steel more easily. I trawled eBay for a few months looking for good deals on Seig C2 and related 7×14 lathes such as Amadel. All these mini-lathes are Chinese made – online consensus seems to be that quality has improved markedly in recent years, but that they still require some fettling to get the best out of them.

After watching several eBay prospects come and go, I saw a Hobbymat / Prazimat MD65 lathe and the BFE mill attachment near to my house, buy it now asking price was similar to lathe only (£400). The mill came with the block to mount it to the lathe, and also with its own substantial milling table. A few calls to engineer-type mates and some googling confirmed that this was a good model, and the range of accessories made it a good buy. So I bought it.

The guy I bought it off owned it for two years but used it only twice. He bought it off an old boy who was retiring from model engineering.

It came with a range of accessories including the small t-slot milling table that attaches to the cross-slide, plus a 4-jaw chuck, several drill chucks and an assortment of arbors and mills.

Lathe 1

Above is a pic of the lathe and mill – the mill table weighs more than the lathe and mill head combined. That’s my Nauty daughter – there was much turning of handles and reading of numbers, while I hopped about nervously (“don’t touch that”). Here she is standing by receive the engineering knowledge of lathes that I had amassed during my three hours of ownership: “it’s very heavy”.

About the Hobbymat / Prazimat MD65

The MD65 was made in East Germany, the date stamps on my machines are 1989. There is not a lot of info about these machines online compared to other makes – I could not find anyone who had published information on a full CNC conversion. Apparently the East Germans sold them at a loss to bring hard currency into the country, after reunification quality went down and eventually they were no longer made as they were not profitable. They were sold under the brand Prazimat in the USA and Hobbymat in the United Kingdom.

I like it that these machines were made in the year the Berlin Wall came down – I imagine that the people who made my machines were hopeful about their future.

Although MD65s are not made any more, these are very similar to the SD300 which is in production (sold in the USA and in the United Kingdom). Parts are available in the United Kingdom via Essel Engineering.

There is an excellent summary available at www.lathes.co.uk.

There is also a Yahoo Group for these lathes: prazi-machining. This group was created after the owner of the original group Prazi_mill_lathe no longer maintained it. There is good info in the archives of both groups, but new posts should into the active group. Yahoo in general, and Groups in particular, appear to have been designed by people who don’t like other people – its un-usability is the product of evil genius.

Owner reviews: www.glue-it.com and www.mike-willis.com.

Adding a auto carriage stop: www.model-engineer.co.uk.

Some information on a CNC conversion using the existing leadscrew (not ballscrews), some plans and photos of disassembly but no pictures of the finished product: danielbauen.com

Disassembly and cleaning

I bought a manual off eBay (seller: fazerblazer), which was nicely bound with a plastic cover, and contained very helpful exploded diagrams.

The lathe was caked in dried grease and metal chips – a combination of brass, aluminium and steel. The previous owner was a big fan of grease – white, grey, black. The leadscrew was coated in sticky white grease, and even the oil holes in the cross and top-slide were packed with grey grease.

There was some surface rust on various parts but none on any of the ways, and it all came off easily with a little WD40 and a green scourer.

Lathe 3

Underneath the filth and staining the lathe was in good condition.

Lathe 2

The leadscrew had a coating of sticky white grease.

Lathe 4

The gearbox was as dirty as the rest of the lathe but again in good condition – no missing or broken teeth on the nylon gears. That’s my Nauty son.

I cleaned most parts with petrol and a toothbrush, or WD40 and a rag. Petrol is smelly but really cuts through thick grease. I used petrol to clean the tailstock block and main carriage – this is verboten! according to the manual as it may dull the paintwork, however I noticed no ill effects. To remove surface rust on steel parts I used WD40 and a green scourer. I used pipe cleaners and a small bottle brush to clean out the holes. I used a can of compressed air to blow gunk out of holes – not as good as a proper compressor however mine is buried in the garage (oh for a proper workshop…).

I was not sure how to clean the ways, which on this lathe is a solid block of round steel with a flat milled on top. I gave the end an experimental light rub with a green scourer, and found that it left visible scratch marks. So, I stuck with a toothbrush, a rag and WD40 to clean the way – it still has some staining but at least I wasn’t going to damage it. There was a ridge of gunk on the underside which corresponded with the pinch gap in the main carriage.

The way had some small dents where sharp tools had been dropped on the top, however it looked like these had been stoned flat as I could not find any raised areas (also the bore of the toolpost slide was not scored).

Disassembly was straightforward except for removing the leadscrew, which proved to be a pain. The taper pin in the gearbox side of the leadscrew was bent in place, and moderate tapping would not release it (from both sides, as it is indeed tapered). In the end I drilled it out.

The next challenge was the little wire c-clip that sits under the inside part of the dog clutch. Could not get it off despite extended swearing – in the end I used some pins out of Mrs Naut’s sewing box to carefully lever up one of the ends. I worked around with a small screwdriver, and the clip was off.

I disassembled and cleaned both chucks (3 and 4-jaw), lubricating with silicon spray. The 3-jaw was in great condition. Some of the threads on the 4-jaw were pitted and chipped, so I cleaned them up with a small file. Also one of the jaws was binding about halfway in, I used a file again to remove a little material from the jaw which made it run easily in the chuck body.

The manual advises against unscrewing the chuck face plate, because if it is not re-assembled correctly there could be problems with alignment. As the main spindle spun well, and I didn’t have the correct C-spanner to undo the two locking rings on the gearbox side, and because the former owner was a grease fiend, I didn’t remove the main spindle. It is easy enough to get to if needed, and I was keen to get back to a working machine.

Rebuild and lubrication

My engineering-type friend Rob recommended giving everything except the ways a coat of silicon spray. Chips will tend to slide off silicon, instead of sticking as they would with grease or other oils. Silicon is also a great rust protector, and is odorless (very important for me, if I want to continue to keep the lathe in the house). I have read that silicon spray should not be used for wood lathes as it mars the finish. I followed Rob’s advice. For oiling the leadscrews and dripping down the little holes in the leadscrew bosses, I used ‘3-In-One’ oil.

For the ways I bought some ISO 68 way lubricant off eBay (seller: out-of-the-game). Online consensus seemed to be that hydraulic oil, chainsaw oil or compressor oil would do, but proper way oil was better. It was about the same price as motor oil so there seemed no reason not to use the good stuff. I applied it using a 6mm paint brush, a thin coat only but making sure I got into all the nooks and crannies.

Oils

The Gang of Four – awaiting the firing squad. Just look at that WD-40 with its fancy ‘smart straw’ – used only for cleaning and not for lubrication.

Reassembly was fairly straightforward. I had a couple of false starts around the change gears and main leadscrew power dog clutch, where I had assembled in the wrong order and had to start again.

The only real ‘gotcha’ I found was tightening of the four bosses behind each of the four handles (main leadscrew, cross-slide, top-slide and tailstock). The cross and top-slide bosses are secured with two cheese-head screws, the tailstock and main leadscrew bosses are secured with four cheese-head screws.

Boss and backplate

Who’s the Boss? And why does he/she look so sad?

What I found is that the tailstock and cross-slide leadscrews ‘galled’ on the inside bore of the bosses. This first happened on the cross-slide the first time I wound the handle all the way in. As the cross-slide got near the end of its travel, the handle became harder to turn. I stopped and checked that the gibs were not tight, but when I tried to turn the handle again it was stuck – I ended up using some heat and gentle tapping to free it from the leadscrew.

Close inspection showed that a chip of metal from leadscrew shaft had come up and dug into the boss (I cleaned up both surfaces with a fine file and emery paper). At first I cursed myself for not properly oiling, however even soaked in oil the leadscrew began to bind again as I wound the cross-slide closer to the carriage.

Galling leadscrew

I guessed that because this was happening only as the leadscrew was wound all the way in, that there was some misalignment between the nut in the base, and the boss in which the leadscrew rotated. This was causing the leadscrew to bend and put pressure on the boss in which is was rotating. There are no bearings in any of the leadscrew assemblies (apart from a brass bush for the main leadscrew, mounted inside the headstock). If I wasn’t planning on converting to ballscrews then I would consider machining recesses in each side of the boss for a small thrust bearing.

This misalignment was caused because I tightened the backplate and boss screws to the top part of the slide (e.g. the cross-slide) before I screwed the leadscrew into the bottom part of the slide (e.g. the carriage).

To avoid this problem:

  • assemble everything and screw the leadscrew in
  • slacken the cheese-head screw on the boss and backplate, so that they can be moved (the tailstock and main leadscrew do not have a backplate)
  • wind the leadscrew all the way in (see pic below)
  • wiggle the backplate around and roughly center it on the leadscrew (by feel) – gently nip up the screws, then gradually tighten making sure not to disturb the positioning of the backplate
  • repeat the above for the boss

all the way in

In case you don’t know what ‘all the way in’ means…

Tooling

I bought an 8mm HSS tool set from Chronos. The lathe came with a boring bar with a removable 3.15mm tip (yes this is probably 3/17th of an inch or somesuch nonsense – up with metric!). I also bought some cutting fluid – CT-90. I have no idea how good or otherwise it is, but it was widely available on eBay so I guess it is at least commonly used.

I also bought some round stock – aluminium round and tube, and some mild steel. This stuff is not cheap! Must find a local supplier. Also must try not to think about all the bits of metal I have discarded over the years…

Next steps

I really enjoyed the rebuild process, there is something very satisfying about cleaning and oiling a machine. The whole process described above took about 40 hours.

Check out the other pages under MD65 Lathe – I have made several modifications and over several years of almost daily use I’ve found this to be a very useful little lathe

 

24 thoughts on “Lathe rebuild

    1. bazmonaut Post author

      Hi Vince – tailstock taper on the MD65 is 1 Morse Taper (1MT or MT1). I don’t know what it is for the SD300 however I would guess it’s the same, and you can find out for sure using the links at the top of the article.

      B

      Reply
    1. bazmonaut Post author

      Thanks Andy – yes I had been looking at the ER25 collet chucks.

      I am in two minds whether to proceed with the original plan to fit an angle plate and mill on the lathe, or just mill on my (in-need-of-TLC) mill. The mill is in my garage and so largely inaccessible, while the lathe is in the house and available for the 15 minute blocks of time I generally get to work on projects.

      Am in a bit of a quandary about the taper size too – the mill (BFE65) is 1MT, while the lathe is 2MT. This seems a bit odd to me but I guess the lathe taper is larger in order to accommodate a larger diameter spindle bore (12mm on this machine). The mill came with a half-dozen or so 1MT arbors of different sizes, which I would like to use on the lathe if possible. I have bought a 2MT to 1MT sleeve, with the idea that I will ‘standardise’ my tooling to 1MT – and use it on the mill and also the lathe via the sleeve.

      However the sleeve does not have a through-hole for a drawbar… eh, the subject of another post methinks.

      B

      Reply
      1. Greg

        Bazmonaut- I just picked up a prazi like yours, similar story on rust and junk coating lathe. Most everything cleaning up well, but I have run into a challenge you may be able to assist me with: I cleaned up the main bed / rail as best I could, then thought to myself: This would be easier if I take off the tailstock and carriage. So I removed the plate at end of the bed and was able to pull the tailstock off. The carriage was tight though, so I ran the carriage to the end with power feed until it came off the nut. Now the carriage is still tight, so much so that I am unable to budge the darn thing. I have opened up the clamps with 1/4 turns on forcing screws… no go, still stuck. Currently soaking in Kroil, will try some more tomorrow. Any suggestions would be greatly appreciated.

        Reply
        1. bazmonaut Post author

          Hi Andy – will check out your rebuilt site.

          About the taper, if you don’t have one then you must have a non-standard spindle – even the ‘new’ SD300s have a 2MT in the spindle.

          B

          Reply
  1. John "Jack" Bonfoey

    Nice job documenting your rebuild. You have a good sense of humor, so it was fun reading what could have been less interesting. I’ve bookmarked you site and will visit again. I bought an SD-300 couple years back and have been in the learning process as I have no machining experience.

    Reply
    1. bazmonaut Post author

      Hi Jack – thanks for the nice words.

      I am learning too – I don’t have any machining experience either (apart from the pillar drill). It’s all great fun – can’t wait to actually make something…

      I do have access to a couple of ex-machinist mates which is really handy. Also I am indebted to people who take the time to share their experiences online – I thought it was time to give something back!

      I will keep these updates coming.

      B

      Reply
  2. buster

    I have a hobbymat md65 lathe and was wondering if you have a wiring schematic of it or a photo of the terminal boards. the book I have that came with the machine shows one thing but I think something is amiss. here is my problem. the electric motor is a capacitor start and has a centrifugal switch on the end, this thing has broken twice so I want to by-pass the switch and add a push button externally to start the motor. it should be simple but it seems the motor is not up to speed. thanks buster.

    Reply
    1. bazmonaut Post author

      Hi Buster

      Sorry to hear that you’re having problems.

      I don’t have a pic of the terminal board, but it is a fairly simple thing located behind the switches. You need to unscrew the cover plate from the bottom of the lathe however, so you’ll have to roll it on its side or prop it up.

      Here’s some pics from my manual, with circuit diagram and also the motor itself.

      Wiring diagram

      Motor wiring

      B

      Reply
  3. Scott

    Hi,

    I’ve got a Prazi MD200… much smaller version of your lathe… Anyhow I was moving it today and dropped it about a foot onto the floor.. the impact was enough that the cross slide cam loose and now I can’t find the gib anywhere… I’ve searched everywhere!

    Is your cross slide gib metal or plastic? I’m having a heck of a time finding it on the floor. If you happen to have a pic of what I should be looking for I’d appreciate it if you could post it.

    Thanks
    Scott

    Reply
    1. bazmonaut Post author

      Hi Scott – the gib strip will definitely be metal, however the MD65 doesn’t have a cam lock on the cross-slide so maybe the two lathes are not so alike. The gib strip is a thin piece of metal as long as the cross-slide dovetail, and about 4mm thick and 10mm wide.

      Hope you found it!

      B

      Reply
  4. Simon

    Quick question in regards to the gear wheel cover, if I screw it on via the hinge at the rear then the door won’t open due to the gear wheel bracket not being flush at the front – I notice in pic (lathe-4) with the naughty son yours is in a similar position – any advice please? Or do I just ignore the hinge and lift on and off as required?

    Simon

    Reply
    1. bazmonaut Post author

      Hi Simon – the cover sits behind the gear wheel bracket. It acts as a kind of latch. I generally run with it open but there are times when you want to be able to close it, like if you’re doing a messy job.

      B

      Reply
  5. Len

    I am looking for the PRAZI SD300 Lathe BRONZE NUT of the Lead Screw replacement. Does anyone knows where I could get it?

    Reply
  6. steve thorpe

    hi i have a md65 and accidentally turned the direction knob and the lathe triped out shed
    now when i turn it on it trips out the shed
    is it the motor shorting out and is it repairable many thank

    Reply
    1. bazmonaut Post author

      Hi Steve

      Sorry to hear about your troubles – I don’t know what damage has been caused but as a first step I would suggest flipping the lathe over and having a look at the wiring behind the switches (there is a simple metal plate covering them from the bottom). You *may* just have created a short in the wiring. I would also suggest bypassing the reversing switch (the one you accidentally flipped) to see if that’s the trouble.

      Beyond this I don’t have much advice I’m afraid. The previous owner of my machine wisely drilled a hole through the motor direction switch and put a pin through it – so you can only turn it if you remove the pin. This is very wise as the switches are exactly the same and easily confused… as you well know.

      B

      Reply
  7. DaveC

    Bazmonaut- a customer of ours passed comment to me that he had a yellow lathe and drill sitting in the back of his work shop which hadn’t been used in a very, very long time , MD65 LATHE and a bolted on BFE mill, cost £200.00 + £40.0 delivery. lead screws look good but the hand wheel is tight, compound is very tight as in no backlash, cross slide nearly 90 degrees backlash gib screws are a mixture.

    rebuild the cross slide or convert to ball screw, I fancy ball screw so any advice or product info would be a great help, did you have access to a second lathe to alter your one to ball screw/cnc.

    Reply
    1. bazmonaut Post author

      Hi Dave – I am a little late in replying (like, months late), apologies.

      That sounds like a VERY good deal for the lathe mill combo. However, I would advise against milling on the lathe as it is not a pleasant experience, the lathe is just not rigid enough.

      These little lathes are incredibly capable for their size. My machinist friends who are used to working on much larger machines are regularly amazed by the capabilities of my little yellow friend.

      Ballscrews are overkill IMHO unless you areconverting to CNC, and even then I would question the need. The main leadscrew is notoriously difficult to turn as it lacks any effective thrust bearings. I installed small needle roller thrust bearings on both the main leadscrew and the cross-slide. These improvements transform the lathe, improving feel and making it much easier to be precise.

      The write-up for the thrust bearings is here: http://www.bazmonaut.com/machines/hobbymat-prazi-md65-lathe/leadscrew-thrust-bearings

      Hope you bought it!

      B

      Reply
  8. Thomas Welch

    Hi! great write up.
    I have a MD65/BFE65 that I purchased in 1994. It has served me well. I mostly machine small parts for model aircraft. (hobby out of control!).
    Recently, I have had two failures with my machines, the lathe carriage has seized and will not move and one of the fiber gears in the mill head has sheared coupling dogs.
    I have been searching for replacement parts with out any luck here in the US. I originally purchased this from IMG and although they have a web site, I cannot get any response. I am nervous about tacking disassembly of the lathe and thinking about taking it to a professional. However, if parts such as a bronze nut are not available then they will have to machined. Do you know of any source for parts?

    Reply
    1. bazmonaut Post author

      Hi Thomas

      Yes there is a list of parts suppliers on this page: http://www.bazmonaut.com/machines/hobbymat-prazi-md65-lathe/

      With the lathe carriage, there are two pinch bolts and one push bolt at the back – i think the push bolt is in the middle. If you loosen the pinch bolts and tighten the push bolt it should made the carriage loose on the ways. If it still won’t move then your issue is with the leadscrew – suggest disassembling the leadscrew handle as a first step, and check for galling. I suspect this is the issue. See my article on adding thrust bearings to the leadscrew handle.

      The link above includes a downloadable copy of the manual, which will help. If the above doesn’t fix it suggest removing the leadscrew – it is not difficult or dangerous. New nut would be easy for a machine shop to make, but I think you’ll find a part from one of the suppliers.

      Mill head gears do go if abused. Did you experience a crash? I don’t know how easy they are to find as replacements.

      Suggest joining the Yahoo group mentioned in the link above – someone may be able to help.

      Best of luck

      B

      Reply

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