Many, very many small lathes have two rolling element spindle bearings that are 62mm outside.
Most have Morsecone 3 and 20mm through-bore because middle part of spindle where bearings sit are 30mm.
I have got a very well made WM180 from Kaimac and have put in a homemade spindle using bearings that are 40mm inside, 62mm outside.
Then cameout of the blue on ebay an affordable , similar size lathe with 38mm hole.
I was tempted and fell in and deserved my ponitense.
Quality is lousy and I ofloaded it very cheap after full explanation of ils.
Am still on friendly terms with buyer.
My son has always doubted my sanity and now he fears for his heritage.
He has no need for my beloved Kaimac 180 (that he removed from here) next three months ,as he is renovating house.
He came up with a good solution and that is I get the Kaimac 180 back for rebuilding.
When that is proven a resounding succes I will then be allowed do the same to my very good quality made HBM250 (920 clone) that also has 62mm bearings.
He will then liberate it from this house of known lathe mistreating.
Problem has been lack of an extra lathe to rebuild one.
Now I have two lathes.
The idea is to change as little as possible and maximize spindle stiffness between bearings.
It is my expirience that many younger lathe owners have to be very carefull to drag a new,younger and bigger lathe home.
The Changes I propose can be very cheap.
Sizes once more:
Originall minis have MC3/20mm bore and runs in two 30/62 mm bearings.
My Kaimac mini was rebuillt and have ER40/30mm bore and runs in 40/62 tapered roller bearings.
My HBM 920 clone has MC3/20mm bore and uses 35/62 mm bearings
Both are being rebuilt with 40/62 mm on the far end where 30-32 mm stock can pass and something very much bigger the front/chuck end, but still without doing anything to the invaluable, holy chineese cast iron of headstock.
Active sections of spindles can then be roughly 42mm inside and 50 or bigger outside.

Picture shows standard minilathe left end with 20mm hole and 30mm bearing seat.
Edited By Niels Abildgaard on 23/01/2020 21:09:05