MVII motor belt length

[zenman]

What is part number fir the new belt.

[JPG]

What is part number fir the new belt.

Assuming you are referring to the Advance belt,

http://shop.advanceautoparts.com/p/dayco-top-cog-gold-label-v-belt-top-cog-17305/19270473-P?searchTerm=17305

[JPG]

Much has transpired since I last posted to this thread almost 4 months ago. This thread has evolved in to a collection of multiple problems and their correction but they all relate to proper speed control, and the most significant contribution to that is the motor belt.

The correct length is 30 1/2 inches, but that requires a 17/32 inch belt which is not currently obtainable.

Wear issues with the control sheave, floating sheave, speed control dial and cam have been addressed during the intervening months.

'New parts were obtained(at least better ones than what I originally had).

The cnc produced aluminum cam was apparently modeled after a warped plastic cam(warp and all!:(). I ended having to remove up to 1/16" from the rear edge of the cam(more at the slow end due to the warp. The aluminum cam that came with the VII from the PO did not have the range(cam lift) of the cnc one.

As mentioned above, the narrow belt did not provide the proper speed range. I added a simple additional idler 'pulley' that also provided additional clearance between the belt and the gear rack. It also compensated for the speed range shift caused by the narrow belt.

Worn parts replaced were: motor shaft key, floating sheave(worn keyway), control sheave(loose bearing/cam follower). The speed control knob securing method was changed so as to remove excessive play and added shim washers the shaft to properly position the idler sheave.

I will be adding several pix to show the effect of these changes as well as some details of those changes.

I stated earlier that I considered proper operation of the speed control to be when the speed is adjusted over its full range, the motor belt moves from the periphery of the idler pulley at slow(700) to the same position on the motor pulley at fast(5200).

Control Sheave with the speed set to 700

[ATTACH]26316[/ATTACH]

Motor pulley with the speed set to 5200

[ATTACH]26317[/ATTACH]

Additional(very small) shimming of the idler pulley on the idler shaft would even them out.

I continue this tomorrow.

[skou]

Interesting info, but currently, to me, academic. Only because I don't have a MkVII. (Yet!)

But, if I ever get a Mark series Shopsmith, the Mark VII will be at the top of my list. If, for no other reason, than the "individuality" of that model. (And, as a kid, my next-door neighbor had one, and my brother and father thought the plastic speed control was a MAJOR flaw.)

JPG, thanks for ALL you've shared on this machine!

steve

[JPG]

The positioning of the idler sheave along the idler shaft contributes to the actual speed range attained. Assuming the speed control knob/shaft/cam and belt are constant/correct, moving that position will shift the speed range. Positioning it towards the control sheave will cause a shift towards a slower speed range(pulley closed). Positioning it away from the control sheave will cause a shift upward to the speed range(pulley opened).

The hub length of the idler sheave will vary the location of this sheave. The idler sheave that came with this MVII was almost 1/8" shorter due to wear(?). Since the sheave rotates with the shaft(keyed) I do not understand how that wear occurred.

However the belt width(as well as length) also affects the speed range. A narrow belt will shift the speed range upward. So adding a shim between the bearing retaining c-clip and the idler sheave hub will help compensate for the thin belt and lower the speed range.


I added machine bushing washers totaling about 0.145" * to position the idler sheave closer to the control sheave. This causes the belt to ride further out towards the periphery of the pulley and thus decrease the quill shaft speed for a given control sheave position. This seems excessive to compensate for a 1/32" belt narrowness considering the belt/sheave geometry, but I have not delved into that enough to justify it. That amount of shimming yielded nearly the desired result with the parts at hand. See *.

Machine bushing washers were used as they have an accurate id. I obtained some from different sources and the thickness varied.

* In the end only one bushing was used yielding a 0.072" shift towards the control sheave.

The thin ones were obtained from HD.
[ATTACH]26327[/ATTACH]

Another thing to consider re positioning of the idler sheave is the positioning of the idler pulley to the motor pulley. The movable sheaves move about 1" over the entire speed range. As the sheaves open/close, the nominal position of the belt shifts axially. The movable sheaves are on opposite 'faces' of the pulleys. When the moveable control sheave is closest to the fixed idler sheave, the floating sheave on the motor pulley needs to be coplaner with the fixed idler sheave. When the idler pulley is 'open', the control sheave needs to be co-planer with the fixed fan sheave. This allows the belt to run in a plane parallel to the pulleys regardless of the speed setting. Eye balling all this after adding the shims does not reveal a noticible belt path deviation. Tis difficult to measure the pulley locations relative to each other accurately with it all assembled.

[JPG]

Over the past few months getting the speed range correct on my MVII has been quite a hassle. Worn parts made finding the right corrective action elusive. The following describes that wear and some effects.

Floating sheave and key.

The floating sheave key way was worn on the floating sheave that arrived with the MVII. As I was trying different length belts with internal cogs, they kept getting snagged by the sheave vanes(no doubt due to trying to get slower speeds). Even after finally getting the correct length they still tended to get snagged. So the floating sheave was replaced along with the key. I obtained the keystock locally at the only real hardware store locally(special order) for a couple of bucks a foot(1/8"). Cut to length.

Control sheave.

The jb welded sheave did not survive all the in/out/futzing with the parts. I replaced it. I may try a different approach to fixing it(welding/machining). It worked even with the bearing not secured, but I did not want to run the risk of it coming out while running.

Speed control knob and shaft.

This was the most demanding, frustrating thing over the summer. The double d bore in the knob had play between it and the double flat on the shaft. It was not much, but resulted in the knob pulling away from the bullet detents. That causes the 'automatic' self adjusting towards fast due to vibration feature that was not intended. This was made worse by my incorrectly assembling it earlier(remember that non-oem spring washer?) that resulted in the corners being worn off the high points on the back of the knob.

After fruitless attempts at shimming the knob/shaft I decided upon more drastic action. I drilled and tapped a hole in the end of the shaft. I added washers and a screw to take the place of the original shaft groove and retaining ring.

[ATTACH]26329[/ATTACH]

Notice I added washers beneath the screw heads(new screws) and retapped the hole that the sheet metal screw was in. The washers were filed down to fit in the base grooves.

I will add a pix showing the of back the knob and the washers after I tweak them. For now there is a washer that fits into the depression on the front of the knob and a couple others to allow the screw to press against the knob face. I will be changing that to allow the logo cover to fit over them.

Here it is.

The small washer is a tight fit into the knob depression and over the shaft. Not sure it is doing much, but it's intent was to help keep the knob aligned with the shaft. The large washer has a counter sink swagged/drawn for the flat head screw. The screw is under cut slightly(filed) to allow a lower profile to clear the logo that clamps onto the the inner edge of the three 'slots'.

[ATTACH]26365[/ATTACH]


Added 'idler pulley'.

Now for something radically new. I added an idler 'pulley' that bears against the outside of the v-belt This partially compensates for the narrow belt as well as increases the belt to gear rack clearance. It consists of a narrow piece of cherry spanning the headstock at the inset for the motor pan top. It is attached to the casting at the overlap and is covered by the motor pan. Drill and counter sink holes(two) at each end in the casting and two flat head screws into the ends of the cherry . A screw mounted perpendicular to the cherry and perpendicular to the plane of the belt mounts 5(five) small bearings(band saw idler bearing stock) stacked.

The reason for 5 is to accommodate the axial positioning of the belt as the speed is adjusted(4) and one to position them all(a spacer).


Belt position on new idler at 700
[ATTACH]26330[/ATTACH]

The belt in the background is riding on the pulley.

Belt position on new idler at 5200
[ATTACH]26331[/ATTACH]

Overview of new idler mount
[ATTACH]26332[/ATTACH]

This also increases the belt wrap around the motor pulley.

[JPG]

Here are more details for the bearing stack idler pulley.

Here it is external to the headstock. I made barrel nuts out of cable clinching hardware.
[ATTACH]26421[/ATTACH]

A pop can sleeve increases the threaded 1/4-20 screw closer to bearing id of 7 mm and eliminates the thread bumpiness.
[ATTACH]26422[/ATTACH]

Two counter sink holes bored in the headstock lip that the motor pan covers. I am not concerned with the screws backing out since the motor pan will limit that.
[ATTACH]26423[/ATTACH]

A unanticipated detail. The mounting block interfered slightly with the power switch. When I initially routed this, the barrel nut was 'there'. It rotated slightly so I had to file it down after putting it back. Fortunately the aluminum was quite soft(intentionally malleable for its original intended purpose) so the router bit survived.
[ATTACH]26424[/ATTACH]

No pix, but the nut(see first pix) securing the long bearing shaft screw was loose. I have since counter bored the cherry to allow use of a jam nut to prevent reoccurrance.

[rcplaneguy]

Very cool!
Congratulations for finding a solution for the belt/speed issues.

[n240sxle91]

JPG,
How did you ascertain the correct location of the idler pulley on the cherry board?

I love how this completely removes the gear rack wear, but I'm having trouble understanding how it affect the speed. I can see how the pulley affects the length of the belt, but I'm missing how it affects its width. What am I missing?

[JPG]

JPG,
How did you ascertain the correct location of the idler pulley on the cherry board?

I love how this completely removes the gear rack wear, but I'm having trouble understanding how it affect the speed. I can see how the pulley affects the length of the belt, but I'm missing how it affects its width. What am I missing?

With a 'normal'(proper width) belt the belt should run about 1/8" below the outside rim of the pulleys at the slow/fast settings.(at fast the belt runs near the motor pulley rim and at slow the belt runs near the idler pulley rim.

When the belt is narrow(as they become with wear) the speed range increases as the belt drops down away from the rim. The same thing occurs with the Mark 5/V.

As for where to position the idler, it was done essentially by trial and error while observing the extreme position of the belt at the speed end points(fast/slow). The goal was equal belt to rim spacing on both pulleys.

IIRC the belt ended up slightly above the rim.

Keep in mind it is a balancing act between too far above the rim, and too far into the pulley where the vanes will cause the belt to jam.

Also realize the control sheave controls everything and the floating sheave merely reacts to it.

If you are satisfied with how a particular belt performs, the idler is not necessary. To prevent belt slapping the gear rack, a shield could be made.

I think the belt slap is a design oversight and should be prevented if possible.