0.0012-0.0014" spindle deflection ok? Old heavy/wide 9

hi all, working on the last bits'n'pieces on my 1929 SB9 (382R). When I took the headstock apart for cleaning and fitting a new belt the front/ chuck bearing had a brass shim (0.0035" thick) around it. Both bearings are one piece bronze with removable top caps with oil cups. When I tested spindle deflection it was in the 6-7thou range, using a dial indicator in a holder stuck to the bead or gear box and a 2ft 5/8" bar. With the top caps removed there was a clear gap around the bearing, between the headstock casting and bearing, and it was easy to move it back and forth perpendicular to the spindle.

Once I added the shim back, plus a thin shim on top of the rear bearing, I tightened the front bearing cap down to tight'n'a little bit, then used the DI on the gear train end of the spindle to torque the rear bearing cap bolts down until deflection stopped decreasing.

Numbers front and rear are 0.0012-0.0014" using the prescribed method. A hand spin of the spindle pulley gives 1/2 a rotation (no chuck mounted). I then ran it at 300, 500 and 1000rpm each for 5 min or so. No issues I could find, bearings didn't heat up that I could tell. Oil quite happily made it out of the cups, through the bearings and out the bottom.

Is that amount of deflection ok? It's more than recommended (0.0007 to 0.001") but I don't want to over tighten the bearings either.

How does it cut under power?

Deflection is bending. What you are describing is oil clearance between spindle and and the two caps.

Deflection is more of an issue where there are more than two caps/journals, like a headstock only has two journals. Think of a 12 cylinder engine. It has 7 main caps/journals. The bore through all 7 caps needs to be in a real straight line. Depending how engine is bolted down, The block can bend or twist. That twist in turn could put pressure on crankshft, to check that, you take a deflection reading. To see if crank shaft is bending. That bending is called deflection. There are other factors that can cause deflection, but you get the idea.

On an old lathe like yours I would prefer a hair more than .001" oil clearance. The reason is the old cast iron of headstock has probably changed over the years, slightly. Anything under .002" is fine.

Besides oil clearance, you can also check thrust. Which is shoving chuck side toward gear side, then back again. .001" is ok there, but going less is also ok here. I like .0005".

those numbers are great...even slightly tighter than what i would shoot for on a machine of that vintage....once under power and that oil film distributes itll be rock solid

jim rozen said:

How does it cut under power?

Click to expand...

don't know yet, making tool holders for the QCTP is on the list

texasgunsmith said:

Deflection is bending. What you are describing is oil clearance between spindle and and the two caps.

Deflection is more of an issue where there are more than two caps/journals, like a headstock only has two journals. Think of a 12 cylinder engine. It has 7 main caps/journals. The bore through all 7 caps needs to be in a real straight line. Depending how engine is bolted down, The block can bend or twist. That twist in turn could put pressure on crankshft, to check that, you take a deflection reading. To see if crank shaft is bending. That bending is called deflection. There are other factors that can cause deflection, but you get the idea.

On an old lathe like yours I would prefer a hair more than .001" oil clearance. The reason is the old cast iron of headstock has probably changed over the years, slightly. Anything under .002" is fine.

Besides oil clearance, you can also check thrust. Which is shoving chuck side toward gear side, then back again. .001" is ok there, but going less is also ok here. I like .0005".

Click to expand...

oil clearance was what I was trying to test, just thought it was called the spindle deflection test. What's the best way to test thrust clearance? When I put it back together I tightened up the collar at the end of the spindle until the spindle started dragging noticeably then backed it off a hair.

iwananew10K said:

those numbers are great...even slightly tighter than what i would shoot for on a machine of that vintage....once under power and that oil film distributes itll be rock solid

Click to expand...

thanks for the insight. Once I put some hours into it I'll check again, along with keeping my ear open for anything changing after heavy use. I need to put some felt in the oil cups too, keep the crap out and slow down the oil flow a little bit.

when measuring endplay on a bearing when you lift the shaft up with more force as the weight of the shaft you start to bend it already
If you look closely to your indicater while applying force to your cheater bar you notice a rapid movement first end then it slows down
The slowed down movement of the indicator is deflection The rapid movement is endplay
You should measure it dry too Oil makes the reading blurry

Peter

What you did for checking end thrust is good common sense, tightening down and backing off nut. It just does not tell you a number, you're doing it by feel.

For a number, stick a dial indicator pointing right into chuck face. Use screw drivers or pry bars to shift spindle back and forth. Not on cone pully though, as that floats. Indicate and pry directly on spindle.

Peter from Holland said:

when measuring endplay on a bearing when you lift the shaft up with more force as the weight of the shaft you start to bend it already
If you look closely to your indicater while applying force to your cheater bar you notice a rapid movement first end then it slows down
The slowed down movement of the indicator is deflection The rapid movement is endplay
You should measure it dry too Oil makes the reading blurry

Peter

Click to expand...

There was definitely a "centering" action - push down was ~6 tenths, pull up was 6-8tenths, release and it settled back to the starting point. No chance of measuring it dry. Test seems to be doing what it's supposed to though.

texasgunsmith said:

What you did for checking end thrust is good common sense, tightening down and backing off nut. It just does not tell you a number, you're doing it by feel.

For a number, stick a dial indicator pointing right into chuck face. Use screw drivers or pry bars to shift spindle back and forth. Not on cone pully though, as that floats. Indicate and pry directly on spindle.

Click to expand...

I'll give that a shot when I put the chuck back on.