Trials and tribulations with a 7x12 lathe

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modeldozer:
Hi to all,

Finally made some more progress. The spindle assembly was measured and drawn to scale so I could sort out the spacers and bearing covers. New bearing covers were designed incorporating lip type seals. As the lathe is out of commission tool paths was programmed to cut the covers on my CNC router.

The parts also arrived and I went in search of some raw materials. Found a great non-ferros supplier only 20min drive from our home. One of the other members on here from Spain actually gave me the name of the supplier, they even sell off cuts at reduced rates. :mmr:
The mild steel I got from a friend at a large manufacturing plant.

A template was printed and the cover roughed out in a piece of 10mm alu plate. It was set up on the router using my web cam centre finder.

It was then machined.

After deburring and cleanup with the seal installed. An added advantage of the cover is it gives more support for the lay shaft bearings.

Next up is cleaning the spindle and reassembly. The rear cover will be done on the lathe when it is at a usable stage.

Abraham

loply:
Hi Abe,

Looking good! You're probably already aware but another thing to make is a new spacer for the preloading of the bearings on the external rear of the spindle. If your lathe is like mine the original was about 5mm oversized and just spun around like a lunatic when the lathe was ran! (Who on EARTH designed it?!). I made one with a very thick OD so that it contacted the bearing on the largest possible area for even preloading. I had to mill out a gap to allow the key for the gear to sit.

Big suppliers offcut sections are definitely the place to go for materials - I used to buy odds and ends off eBay but it was very poor value - I recently got 60cm of 50mm steel bar (a hefty lump!), and 1.5m of 20mm steel bar, for £10, and he was trying to give me more!

Got about 5 meters of 50x25x5 steel box and two lengths of 30mm and 40mm steel rod for £10 last time too. Can't beat it :clap:

modeldozer:
Hi Rich,

The spacers are actually the reason I drew the assembly, it just did not make sense to me. After drawing it all I actually found that with the normal bearings, spacers and gear assembled, the distance between the insides of the two bearings was 2+mm more than the registers in the housing. With the taper rollers it ends up 0.5mm to short, makes one think. :scratch: I will also be making a fatter rear one from mild steel for the rear lip seal to ride on.(still need to get the length once all is in its place)

:update:
The spacers next to the bearings needed a step cut to clear the cages. They were machined with the CNC router.

Everything was given a thorough cleanup, there was a lot of casting sand still embedded on the inside surfaces of the housing. The “hub” on the spindle where the new seal will ride was polished.
All ready for assembly.

It was then all assembled dry and alignments checked. I took some measurements to make two spacers for the lay shaft to act as stops, preventing over travel of the change gear.
Next I used a method we use in the adjustment of taper bearings in machine transmissions. Between the gear and last spacer two pieces of soft solder is trapped, the preload is then adjusted and all disassembled. By measuring the thickness of the flattened solder the spacer thickness is determined.

Here it averaged out to 1mm, so I made two 0.5mm ones from alu sheet to go both sides of the gear assm. Also rounded over the ends of the shift fork to prevent any foul-ups. A small relief was also made in the fork to clear the shift lever shaft.

Hopefully final assembly is next.

Abraham

ozzie46:

A very timely thread as I just received the bearings to redo my 7 x 12.

You're doing a nice job of explaining things.

Ron

doubleboost:
This machine will be a credit to you :clap: :clap: :clap: :clap:
John

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