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Evaluating step belt B'port head statically? (laying on a workbench)


My step belt head has a bit of backlash when in back gear (holding the spindle and rocking the drive pulley back and forth). In high speed, the backlash is 4 or 5 times as much and the head is quite noisy in operation. A few times with a larger dia. cutter hogging a bit too much, the drive to the spindle literally skipped. I picked up a couple of step belt heads at auction (no motors) for cheap with minimal backlash so I am planning to see if I can cannibalize them for parts. I take for granted there is a problem with both of these heads otherwise they would not have been removed from service.

Now my question - is there any way to statically inspect these two heads (such as play/wear in quill and spindle brgs) - I am wondering if one of these heads might be better repair candidate than the one I have in use. FWIW, one of the parts heads has sealed bearings (I presume, no oil cups) and the 2nd parts head does not have an oil cup for the back/bull gear. What else could/should I be looking into before dismantling? This is for hobby use, only issue is that I don't have mill access while I take my head apart to repair. TIA


New member
The only way to fix or SEE what is worn..

Is to take it apart..

An unknown head should be pulled down, just because. Leave spindle and spindle bearings alone, if they are smooth and quiet...

But your problem is in the belt and gear housing assembly.

That is because it skipped out under load in Hi range,

The Dog clutch teeth, are probably worn beyond fixing on spindle pulley hub, and splined gear hub...

Only other thing causing that, would be missing/damaged springs (4 ea) that push down on pulley bearing sleeve.

Just swap smoothest/tightest feeling belt pulley/gear housing assembly, on your running quill housing..

Just 3 nuts.. Pull Drawbar first of course..


New member
The heads are fully rebuildable so do not throw any of the main parts (housings) out. This is very simple and I believe H&W Machine Rebuilders may have a video on exactly what you need. He has a ton of videos. I referenced one the other day for one I had opened up.


Thank you for your responses.

Since I did not get any responses for several days, I decided to do two checks before opening things up on the core/parts heads. With the quill fully extended and a dowel pin in a collet I put a 25 lb side load on the dowel pin and measured the deflection between the quill to housing. Secondly I tried to check the runout of the spindle. With an indicator on the tapered surface I was getting gibberish so I used a collet and gage pin with the indicator riding on the gage pin. I used the same collet/gage pin in all three heads. Turns out the head I have been using is the worst of the three with respect to spindle runout and quill freeplay. I have no desire to mess with the spindle and its bearings.


New member
A BP spindle is not in the same class, as a 20k rpm CNC spindle..

A couple Pin spanners.

Very clean parts.

To make things even simpler, sealed P4 grade bearings are available.

H&W slaps them together pretty quick in a Youtube vid..

I spend a bit more time, but a BP is a kids wagon wheel bearing job, compared to High rpm High $$$ spindles..

Bearings are $350 ish.... I usually replace everytime I am working on an older, non cared for head...

Swapping complete Quills is not usually an option. Quill housings were honed to match quill..

Since you have spare heads (lucky)

Just mix and match best parts.

Run into problems?

Ask here and watch Youtube..