My Goofy Lathe

[the elephant]

I am slowly getting my lathe into shape so that I can start doing the exercises in this machinist book I bought. I have been using it, but sort of by trial and error. So far I have felt like Tom Hanks in Castaway when he spends all his time trying to catch tiny crabs in the surf, then discovers that raw crab is basically a disgusting jelly, so he learns to make fire, struggles on to survive for five years, then, once rescued and safely home he is at a reception and sees buckets of massive king crab claws, his without effort. It was one of the more poignant moments of that film for me.

My "Castaway Moment" came for me after seven or eight years of struggling mightily with center-drilling and tapping 4mm rod and trying so damnably hard to get the hole centered on the end of that rod, despite forever-walking drill bits and a horrible drill press with gobs of runout in the quill that cannot be repaired or corrected because IT IS A CHEAP POS, the first time I chucked up some of that 4mm rod in the lather for the same operations I was done about ten minutes after I figured out what direction to run the machine and how the cutter needed to be set up in the tool post. It took zero physical effort. It took nearly no time. It was… easy.

Now I want to learn to use it correctly.

So tonight, another night plagued by insomnia, I ended up doing hours of research on several upgrades that will fit and play nicely with this very rare lathe. I bought some of them, too. I love this machine, but it is quite old, out of production for decades now, and rare AF in the US. I can find bits and bobs on UK eBay and from UK machine tool repair shops, but most of it is metric, and my machine is imperial. So only used, only expensive, and only when you search for months first.

It is such a problem that I ended up buying a second machine to have a parts supply for the big things that are impossible to locate otherwise.

So the good lathe is working, but needs some care. The parts lathe is not fully disassembled and is undergoing a LOT of repair or replacement work, and I think that in the end it will be the better of the two machines. I have decided to fully restore both, and adopt the better one for my needs, and the other one will get carefully packed up and stored for future needs.

I have a highly sought-after, collectable lathe with tons of attachments that are also very sought-after items. I love it and see why it is so heavily coveted by collectors. I may clean it up and sell it as a set to a collector to fund more working stuff for the larger one I am currently using.

I'm having some fun with this stuff. It is funny how much I love this sort of work, as I turned it down to be in the beginning band. "How about enrolling in Metal Shop, son?" "Nah, Shop's for losers. I want to be in the band!"

How weird life can be.

[TxTx]

I was lucky enough to be able to take both shop and band, for a while anyway. Also, my dad, a second generation mechanical engineer, was also heavily into metalworking, casting his own lead and bronze sculptures and making steam engines. So I grew up making things on his lathes and vertical mill. I’ve made about three tuba parts so far - a valve cap for my 1928 Martin, and a big valve button and thumb ring holder for my Willson. Fun stuff.

Anyway curious what your exotic sounding lathe is, and happy to share the little that I know about making stuff on one.

Eric

[tofu]

We had to take shop. Band was held before school started. It was actually the first room in the basement in this huge wing of the school and the rest of the wing was shop classes - wood, metal, plastic, automotive, mechanical drawing etc. Those were great classes - I especially enjoyed the smell of the wood classes. We used the lathes a lot and they had a bunch of them. After a few months of classes the instructor specifically asked me to find something to create other than large deadly weapons...


These days the school district completely eliminated the shop classes for both the middle and high schools. Their whole push is every kid must be college bound. It seems completely foreign to them that not everybody needs or wants to go to college or the fact these shop classes taught kids really useful skills that come in handy later in life for things like working on your house or car etc.

My dad had a close friend who was a machinist for one of the airlines at O’Hare and he had the most amazing assortment of lathes lining all four walls in his huge basement. These things were huge. I still wonder how he ever got them down there or how he obtained them as he was about stingy with a buck as anybody. He did the most amazing car restorations in his spare time. I assume they somehow made their way to his basement one way or another from O’Hare.

[2nd tenor]

I am slowly getting my lathe into shape so that I can start doing the exercises in this machinist book I bought. I have been using it, but sort of by trial and error. So far I have felt like Tom Hanks in Castaway when he spends all his time trying to catch tiny crabs in the surf, then discovers that raw crab is basically a disgusting jelly, so he learns to make fire, struggles on to survive for five years, then, once rescued and safely home he is at a reception and sees buckets of massive king crab claws, his without effort. It was one of the more poignant moments of that film for me.

My "Castaway Moment" came for me after seven or eight years of struggling mightily with center-drilling and tapping 4mm rod and trying so damnably hard to get the hole centered on the end of that rod, despite forever-walking drill bits and a horrible drill press with gobs of runout in the quill that cannot be repaired or corrected because IT IS A CHEAP POS, the first time I chucked up some of that 4mm rod in the lather for the same operations I was done about ten minutes after I figured out what direction to run the machine and how the cutter needed to be set up in the tool post. It took zero physical effort. It took nearly no time. It was… easy.

Now I want to learn to use it correctly.

So tonight, another night plagued by insomnia, I ended up doing hours of research on several upgrades that will fit and play nicely with this very rare lathe. I bought some of them, too. I love this machine, but it is quite old, out of production for decades now, and rare AF in the US. I can find bits and bobs on UK eBay and from UK machine tool repair shops, but most of it is metric, and my machine is imperial. So only used, only expensive, and only when you search for months first.

It is such a problem that I ended up buying a second machine to have a parts supply for the big things that are impossible to locate otherwise.

So the good lathe is working, but needs some care. The parts lathe is not fully disassembled and is undergoing a LOT of repair or replacement work, and I think that in the end it will be the better of the two machines. I have decided to fully restore both, and adopt the better one for my needs, and the other one will get carefully packed up and stored for future needs.

I have a highly sought-after, collectable lathe with tons of attachments that are also very sought-after items. I love it and see why it is so heavily coveted by collectors. I may clean it up and sell it as a set to a collector to fund more working stuff for the larger one I am currently using.

I'm having some fun with this stuff. It is funny how much I love this sort of work, as I turned it down to be in the beginning band. "How about enrolling in Metal Shop, son?" "Nah, Shop's for losers. I want to be in the band!"

How weird life can be.

Looking back through your other posts your lathe ( https://www.tubaforum.net/viewtopic.php ... he#p100592 ) is East German, a Prazi Lathe, and it looks very similar to what the Chinese offer now … maybe the design travelled. I’m surprised that it has any Imperial parts and wonder about sourcing parts directly from Germany. In the UK there are suppliers who specialise in supplying ‘model engineers’ with small machine tool parts and helpful literature (magazines and books). Import of goods to the UK from behind the Iron Curtain (pre 1989) wasn’t uncommon and some of the old ‘commi’ businesses managed to survive.

There’s probably an owners association somewhere and many more details to be found on-line. The Hobbymat seems essentially the same and made by the same folks - I think that parts will very likely be interchangeable.
https://www.lathes.co.uk/hobbymat/page3.html

[the elephant]

No to all of this, but thank you. I have been investigating this for years. I am a member of every forum dedicated to this lathe. And yes, the Hobbymat MD65, Proxxon SD300, and Präzi SD300 are all the same machine. The differences between the metric and imperial versions are the thread pitch of the four leadscrews and the gradations on the dials, and the tailstock quill. The euro and US versions are further differentiated by the motors and wiring, one being for 220 and one being 110, of course. I own two Präzis, one each metric and imperial. Parts are difficult to come by unless you buy them from two or three fellows in the UK and Germany, but 95% of what they sell is for 220V metric units. My Metric one is complete, and what I use. The imperial one is being restored, albeit very slowly, as I manage to source parts.

Being from behind the Iron Curtain, the design is pretty proprietary and uncommon. In fact, the design is completely unrelated to the little Shanghai Sieg-made lathes. (Regardless of the import stencil brand, they all are made from the same castings made by Sieg.) It is a cast-iron bed with a trapezoidal guide on two narrow ways, while the East German lathe is a solid steel D-shaped bar with a separate, very heavy base, the carriage and the tailstock sliding along the flat of the D bar as with some of the nicer watchmaker lathes, and the headstock trammed to the flat.

My carriage and tailstock are cast iron, while the headstock case seems to be made of cast aluminum. The metric one has a very thick and heavy aluminum base. My imperial unit has a quarter-inch steel base with the long edges rolled downwards and end caps welded to both narrow ends. It is slightly less rigid than the much heavier aluminum base of the metric unit. It was also made after reunification, so it has much cheaper German and Chinese bearings, switches, and motor, whereas the little communist lathe uses what were at that time the highest quality parts, which, despite the problems in the Communist world with quality, are quite good. The bearings, made in Bulgaria and Czechoslovakia, are as good as the best SKF bearings made today. The older wiring and switches/pots are very simple and robust. The newer one was when the company was desperately trying to compete as a Western concern, and their managerial and production inefficiencies prevented them from keeping up; their quality declined through the use of bargain components, but prices soared when currency controls were removed and wages had to meet Western levels.

VEB Präzisionsdrehmaschinen went out of business a few years after reunification and the fall of the USSR. (1996?)

The design was sold to a Hungarian business in the late 1990s, but they eventually stopped making it because it was too expensive to sell to anyone who wanted such a small lathe, possibly due in part to the super inexpensive Sieg models that were starting to pop up in the backs of hobbyist magazines.

Mine uses larger, sealed, angular contact bearings by design; the Siegs all come with very low-quality, smaller, plain ball bearings, but you can upgrade them to tapered rollers or sealed angular contact bearings to greatly improve the Chinese headstock's runout. The Chinese lathe is a decent design, but you have to pay out more than the whole machine cost in order to make it able to produce accurate, repeatable, MARKETABLE work.

The little Präzi was designed for laboratory work, so it was super-accurate out of the box. It is a little bit larger than the HF lathe, too. Mine weighs in at just over 100 pounds—lots of mass for such a small machine. It is also decently rigid, as long as I don't try to turn or part off face-hardened steel or the more gummy stainless alloys. It is perfect for turning brass.

I did not know you had an interest in lathes. Very cool, sir.

[2nd tenor]

I worked in engineering for many years and gained a reasonable living from it. Doubtless others on this forum have too and will be willing to share what knowledge they have.

You are likely already aware but if not them I’m pretty sure that there were/are inverters (electronic devices) that’ll take (an an input) 110V 60 Hz supplies and give you (output) 240 V 50Hz, so your local supply can be changed to what your lathe might prefer. Just a thought.

[the elephant]

I own a 110V welder, which is excellent, but it is limited to steel of .25" thickness, and that is pushing it. I also own a 110V gas clothes dryer.

I would like to have a larger welder and an electric dryer, so I foresee an eventual addition of a 220V outlet (paired 110V lines, I guess) in the future. If I get this done, I think I'll be able to natively run three-phase powered machines as well as rewired Euro stuff. Is this correct?

[2nd tenor]

That’d be outside of my knowledge base but maybe others might help. As a start point Mary Ann comes to mind, I think she was involved with electronics.

Inverters to change single to three phase were available but they ain’t cheap and they are limited by the available single phase supply.

A local supplied (purchased)110v 60 Hz motor could (also) be coupled and reduction geared (via belt drive and pulley sizes) to your lathe. At one time all lathes had external motors and belt drive.

[the elephant]

I have an Austrian lathe with an external drive with three belts. Too small for much real work, but handy to pick up and set on the bench for quickie jobs when making linkages or levers.

It is very accurate, but not all that powerful, and the motor's duty cycle is low, so a lot of resting is needed to keep it cool. I am looking at replacing it with a brushless continuous duty motor of the appropriate torque and RPM numbers. But that will have to happen later. I also have several old Delta motors that I keep around here in boxes. One of them would work great, but they are single-speed, high RPM. So probably not.

[TxTx]

I would like to have a larger welder and an electric dryer, so I foresee an eventual addition of a 220V outlet (paired 110V lines, I guess) in the future. If I get this done, I think I'll be able to natively run three-phase powered machines as well as rewired Euro stuff. Is this correct?

A 220v outlet is indeed made up of connections to 110v lines of opposite phase (assuming you have 220v coming to your house - think that is pretty universal in the US) but it is still only single phase power. So you could run a single phase welder, larger residential driers, and single phase European equipment as long as it is tolerant of 60 cycle power. Actual three-phase power coming into residences is I think pretty rare though. So most folks seem to use variable frequency drive electronics for that.

Eric

[gocsick]

I ran my large lathe on a VFD... much better than the old rotary phase converters or changing motors to single phase.

[the elephant]

I would like to have a larger welder and an electric dryer, so I foresee an eventual addition of a 220V outlet (paired 110V lines, I guess) in the future. If I get this done, I think I'll be able to natively run three-phase powered machines as well as rewired Euro stuff. Is this correct?

A 220v outlet is indeed made up of connections to 110v lines of opposite phase (assuming you have 220v coming to your house - think that is pretty universal in the US) but it is still only single phase power. So you could run a single phase welder, larger residential driers, and single phase European equipment as long as it is tolerant of 60 cycle power. Actual three-phase power coming into residences is I think pretty rare though. So most folks seem to use variable frequency drive electronics for that.

Eric

Excellent info, sir! THANKS!

[the elephant]

I ran my large lathe on a VFD... much better than the old rotary phase converters or changing motors to single phase.

Okay, my ignorance is on full display right now: What is a VFD? In my rural area, it means Volunteer Fire Department.

[gocsick]

Variable Frequency Drive... It takes your 220V single phase (or 110V if you motor is small enough.. usually around 1 HP max)... rectifies it to DC.. then runs it through an inverter to 3-phase. They are completely solid state and very efficient.

The real utility of them is you can control the frequency of the inverted 3-phase... and since for 3-phase motors the speed is directly tied to the frequency.. you can use them to fine tune the spindle speed of the lathe.. basically it gives you full range between the set speeds from your change gears.

You can also get fancy and use it for things like soft start and custom motor acceleration curves etc. Also they help with power factor correction when running motors at loads sufficiently under their rating... makes a toolroom lathe run in a house or shop much more energy efficient when you are doing things like spinning a piece for polishing or burnishing instead of taking heavy cuts.