Fan sheave set screw

[solicitr]

Thanks, everyone. I found I'm brawny enough to brace one end of the board against my leg and rassle that gator.

Now that I have it off- guess what! No spacer at all! Judging by the multiple set-screw scars on the long key, it looks like the previous owner had this problem many, many times and just kept pulling it out and cranking that set screw. Instead I'm spending seven days and seven bucks for a 70 cent part (grr). I'm going to try to live with my current fan sheave, even though it definitely has a little wobble and I don't like that. (The floating sheave thank goodness has no play whatsoever).

I now have officially dismantled every part of the Mark V headstock, shy of actually pulling bearings. Congrats to me (I think). 2-bearing quill with new ring drive, new power switch and 12/3 cord, all shafts, sheaves, tube locks and the speed control pulled, cleaned and lubed.

EDIT: and the quill spring, too- *that* was one nasty reassembly!

At least I'll know how to do it when those dry bearings start to fail!

[solicitr]

Charlese:

Look around, you might find that spacer in your parts bin. It's a little thin walled pipe, about 3/4" long (plus or minus).

Whoa, whoa, whoooa! Three-quarters? The motor plate and the fan plate are only 5/8" apart!

Just for the heck of it, I tried a 1/2" molding arbor spacer on there- and the sheave was pushed out way too far. So I tried a 1/4" - a good quarter clearance. So for instructional purposes only I tried out the spring-retaining washer (about 3/32")- nice spec clearance all around.

In fact, since it just rides on the inner bearing race, what would be wrong with using a standard 5/8" washer? It might help stabilize an iffy sheave.

[charlese]

...Whoa, whoa, whoooa! Three-quarters? The motor plate and the fan plate are only 5/8" apart!...

That's what I said!:) The key word is about. Maybe - it is about 1/2" long!

When posting, I was trying to remember back several years. Haven't seen that little bugger in quite a while. Heck, I can't remember yesterday very well! Just held my thumb and fore finger apart and took a guess. Sorry If I led you astray!

I have to admire your dedication in getting your machine in working order.

[solicitr]

So now I'm puzzling. Please, people, chime in: what is the vertical relationship between the fixed sheaves (idler and fan) supposed to be? It appears to me that even when the fan sheave is positioned with bare-minimum clearance, there is an appreciable angle in the drive belt, which doesn't seem right. Yet the lower sheave can't get any closer to the motor, and the upper one can't get any closer to the poly-V pulley. Help! What's going on?

[dusty]

Two questions:

Is the relationship now different than before "teardown"?

What parts were replaced/substituted? That is to ask, what parts are there now that were not there in the beginning?

[billmayo]

You are right. With the motor floating sheave going one way and the idler control sheave going the other way, there could only be one speed that both are aligned. Close counts and works in this case. I believe this can cause some vibration when they are in the mis-aligned position. This is another reason why I like to use the Power-Twist (link) belt as it accepts mis-alignment much better than a normal V-belt. Therefore, I only do the Gilmer/Poly-V belt alignment and not worry about this alignment. I did think about switching the motor around but it would turn in the wrong direction then.

Bill Mayo

So now I'm puzzling. Please, people, chime in: what is the vertical relationship between the fixed sheaves (idler and fan) supposed to be? It appears to me that even when the fan sheave is positioned with bare-minimum clearance, there is an appreciable angle in the drive belt, which doesn't seem right. Yet the lower sheave can't get any closer to the motor, and the upper one can't get any closer to the poly-V pulley. Help! What's going on?

[dusty]

First we need to establish some fixed relationships.

The motor (123), Fan Sheave (119) and Idler Sheave (109) do not change relative positions.

On my machine (which has never been torn down) separation between:

1. motor and fan sheave is 3/16"

2. fan sheave and control sheave is 1 1/4"

3. control sheave and idler sheave (@ low speed A) is 3/4"

4. fan sheave and floating sheave (@low speed A) is 1 7/8"

when the speed is increased to high speed (R)

5. control sheave and idler sheave separation increases to 1 11/16"

6. fan sheave and floating sheave separation decreases to 5/8"

The belts are very nearly vertical!

The lower shaft (idler shaft) protrudes from the belt cover 1 7/8"

The fan sheave (119) is fixed as is the idler sheave (109) but doesn't the control sheave (110) move with a speed change as does the floating sheave (117)? this last statement changed by edit at 4:41pm

[solicitr]

The fan sheave (119) is fixed as is the control sheave (110) but doesn't the idler sheave (109) move with a speed change as does the floating sheave (117)?

No, the idler sheave (109) is fixed to the idler shaft with a clip and retaining ring and doesn't budge. The control sheave does all the moving on the idler (middle) shaft, as the floating sheave (117) does on the lower (motor) shaft.

I'll have to check againstall your measurements, Dusty. I know that the idler shaft and therefore the idler sheave are absolutely, positively in the correct position- I verified the alignment of the bearing groove with the eccentric-bushing setscrew hole with a tiny flashlight and much contortion - and it does wind up with the bearing bang flush with the eccentric bushing against the stop-washer.

There's no way for me to tell the 'before' position of the fan sheave, because the spring spontaneously slammed it into the fan plate. It's that that I'm trying to make sure is aligned correctly.

[dusty]

Yes, you are absolutely correct. I have always had this sort of a problem with drawings. When I was a test engineer, I had to be real cautious of my work. A mistake like this would have been costly. The Idler Sheave (109) is fixed in position and the Control Sheave (110) is moved to effect the speed change.

[solicitr]

I've just figured it out! At least in theory, if the parts are correctly aligned the drive belt will be vertical at all speeds!

The key to all this, I suppose, is that during speed changes, as one sheaf-pair or pulley is opening the other is closing. What this means is that the control sheave and motor sheave are always moving in the same direction- as the control arm pulls the upper pulley open the spring closes the lower pulley from the other side, and vice versa.

Now, each pulley has an effective center, the plane where the spokes mesh. This center will move left or right as the moving sheave moves left or right- but since the other sheaf is moving in the same direction by the same amount, that effective centers of both pulleys remain in the same plane, moving left or right together.

Envision the alignment at dead-medium speed: 1 to 1 ratio, 1725 rpm on both shafts, pulley 'diameters' identical and thus sheaves the same distance apart. Imagine also that the two front and two rear sheaves are in exact vertical alignment with each other.

Now start increasing speed. The pork chop pulls the control sheave to the right (operator's POV), the drive belt sinks deeper into the now-wider upper pulley, and the slack is taken up on the lower pulley by the spring pushing it closed (i.e. the floating sheave also moves right).

All these relationships are linear- as the belt seeks a new circumference all the movement is first-order proportional, so that the (lower) floating sheave necessarily moves exactly the same distance as the control sheave, and therefore the 'effective center' or drive belt centerline moves together (at half the rate of the sheaves' movement) on both shafts, remaining in vertical alignment throughout.

Clever, clever man, that Dr Goldschmidt!

Now I just have to turn all this into numbers....