Sticky Nut Problems with Spindle Changes

Lock nuts on shaper spindles can be stubborn and awkward when it's time to change the spindle. Here's how some machine owners tackle the problem. April 29, 2012

Has anyone come up with an improvement for removing spindles on SCMI T-110 (and similar) shapers? I'm referring to the double threaded nut that locks the spindle onto the machine.

We occasionally change between our standard 1-1/4" spindle and a couple others. The SCMI design for this changeover is to unthread the main mounting nut upward until it presses hard enough against a rubber O-ring. The idea is that the O-ring compression will then pop the spindle taper free. Even with anti-seize compound on the taper, this does not work. We always end up having to put a heavy moulding head loosely on the spindle below the nut and slide it upward so it pounds on the bottom of the nut, thus jarring the taper free. Before we get to this point, the nut is usually bound up against the flared end of the spindle, requiring a pipe wrench and a few good curse words to get it free.

I'm thinking of maybe replacing the rubber O-ring (which is pretty much a useless component in the system) with something rigid, durable and slippery, like perhaps a PTFE (Teflon) ring that is hard enough to stand up to the pressure. Any thoughts?

Forum Responses
(Architectural Woodworking Forum)
From contributor L:
We have a SAC shaper with a similar design. Never have figured out an easy way. Luckily, rarely need to remove the spindle. Ask SCM tech help; maybe there is an easy way?

From contributor J:
How about a big wood block with a hole through it that fits over the spindle? Now put a washer or collar and nut on the spindle and try lowering it with the wheel. You might need to tap on the top of the spindle a bit to knock it loose, but it shouldn't take more than that.

From the original questioner:

Yup - done that too, over the years. Just with 2 sticks either side of the spindle instead of one with a hole. I've had this shaper at least 15 years, so there isn't much I haven't done to get that sucker free. Thanks for the suggestion.

From contributor G:
Maybe if you use contributor J's method to put some upward force on the spindle, then give it a whack on the side to simulate side load. Tapers can be disengaged with side load sometimes.

From the original questioner:
In terms of using force, the upward sliding moulding head against a fixed nut seems to work best. It usually jars the taper loose quite nicely. It would be nice to find a way to make the thing work the way it's intended, though. The use of a rubber O-ring to spring the taper loose is ridiculous.

From contributor P:
That spindle connection is called a differential lead design. The different thread leads allow the spindle to actually draw itself out of the socket. It works, but you have to assemble it correctly for it to work. For some reason, SCMI does not mention this... Go figure.

This is how it works, and I have done this probably 50 times with no hammers, no issues. Thread the nut all the way to the shoulder on the spindle. Insert spindle into socket and thread the whole assembly down with your hands on the spindle only (do not turn the nut yet). When it bottoms out, take that big spanner and turn the nut to fully seat the spindle. To remove, back out the nut until it hits the shoulder, keep turning, and it will draw itself out.

There are other Euro machine tools that employ this design. They seem to like it.

From the original questioner:
Thanks. I do understand the theory of the two different thread pitches involved, but it just doesn't seem to work on mine. I've tried it time and again as you describe, to no avail. However, I can't say that I always pay specific attention to the spindle seating in the taper before finally turning the nut alone to lock it down. I will do another swap out and see if I can make it work as it should.

From contributor B:
I have the T-120C, which is the same spindle setup. I found it difficult to change the spindles at first, then realized something I learned in gunsmithing… Your hands have oils, and I did see some marks on the spindle and inside the cartridge, so I cleaned them up with emery cloth, then I began the practice of spraying a light coat of Teflon in the cartridge. I also thread the nut up till it stops before putting the assembly in. This is the first time I've heard about the O-ring. Never saw one on my machine. I did buy it used, though, so I figure it just isn't there. It hasn't been a problem as of yet. I do change the spindle every month or so, depending on what I'm running, so maybe there isn't enough time for the spindle to lock up. Well, that's all I've got.

From contributor P:
I took a closer look at the spindles and socket the other day. Then I remembered I had my primary spindle custom fabricated from 4340 steel hardened to Rc 36-40. The slightly harder spindle is much easier to remove. The stock spindle seems to have the same hardness as the socket, which can cause them to gall. Usually tightly mating steel parts should be of different alloys and be a few points apart on the heat treat if they are bare metal. Not sure what SCMI uses, but they seem a bit soft to me.

From the original questioner:
Good stuff. Thanks. I keep anti-seize on mine and it really doesn't do much good. I even had the taper machined away on the center 2"-3" of the 1-1/4" spindle years ago so it only contacted high and low, and that didn't really help. I did that to repair some damage that occurred during a more than usually frustrating removal of the spindle.

I think part of my problem is I don't change them very often - only a couple times a year. I think that gives the nut a chance to torque itself down and put excessive pressure on the tape. That is a good point about similar hardness metals causing them to gall.

From contributor B:
Had to change the spindle today. It stuck. Darn! Had to do the two stick and crank thing. So much for Teflon! It did pop easy though.