PM1130 spindle taper

[kmanuele]

Was trying to align the tailstock spindle. Had an MT3 dead center, so I inserted an MT5/MT3 adapter in the headstock spindle, but it wouldn't seat onto the spindle taper.

I found that the adapter was bearing on a ledge further in, limiting how far in the adapter could move.

I was able to machine off that ledge, matching the MT5 spindle taper, so the adapter now seats properly. It was a challenge, as that was the limit of my 1/2" boring bar extension. Lots of chatter, and not great finish. But it worked.

Not sure what is wrong here. Spindle taper too wide, that ledge not machined? I am sure that a MT5 dead center would have a similar problem -- if not worse, as they are longer than the adapter.

Anyone seen this problem?

Thanks

 

[jaek]

My SB1007 is similar. The length of the MT5 taper is about 1.75”, then a short relief, then the spindle bore of 1.34”. A real MT5 taper would be five inches long and 1.47” diameter at the small end. Maybe it's short to provide enough spindle wall thickness at the front bearing?

On the bright side, South Bend / Grizzly included a short MT5/MT3 adapter.

 

[kmanuele]

Glad, sort of, it's not just me

At least you have that length of engagement. My spindle taper is barely an inch long. Doesn't seem like enough engagement to seat anything reliably. Design flaw, IMO.

This is what I ended up with. Not pretty, but it worked. That shallow angle required me to bore way in there to get the adapter to seat.

 

[jaek]

Agreed the taper on yours is really short, almost to the point of uselessness.

You can always make a soft center by turning a 60 degree point on a piece of stock held in the chuck. It'll be exactly concentric with the spindle until you remove and replace it, just a matter of taking a quick skim cut each time you chuck it up.

 

[kmanuele]

That's a good idea, as I am seeing some cumulative runout from the adapter and MT3 dead center.

Thanks!

 

[Larry$]

This is a game played to make a small bearing bore sound like a larger lathe. Marketing!
You won't find 1/2 sized MT's in the literature until the Chinese machines started to be imported in larger #s. The small end of a MT should be providing more support and friction than what these 1/2 sized MTs give. That said for hobby or light duty work they will suffice if properly ground. Apparently a big if!
Blue up the adapter and see how much contact you are getting.

 

[tweinke]

Checked my 1130v with the supplied MT5 to MT3 adapter, and it fits perfectly with very little or any run out .