The Bill Mayo Mods - Conventional Headstock

[Maurice]

I'm fairly new to Shopsmith. I've got a Mark V 500 that I'm in the middle of rebuilding, and every time I search the forum for how to do something I turn up another Bill Mayo post with a mod or fix I wish I'd found sooner. He worked on hundreds of these machines and shared most of it here, but it's scattered across dozens of threads and easy to miss.

When I turned up yet another one today I'd never seen (the link belt, below), I decided to pull as many together as I could. Most are from his posts, a few I've done myself (photos at the end).

If I've missed any, let me know.

• Speed control quadrant / porkchop bolt kit. The quadrant roll pin wears its holes in the bracket legs, the legs spread, and the teeth wear uneven until the speed dial jams. Fix: punch the roll pin out (don't heat the bracket, it's a soft alloy) and replace it with a 2-1/2" #10-32 socket-head bolt, 2 star washers and a nylock nut, then centre-punch the leg holes closed so wear stays between bolt and quadrant. A half-smooth/half-threaded (shouldered) screw is ideal; #10-24 works too. Bill ran this in 300+ assemblies over 10 years with no repeat failures, so if you're fitting a new quadrant anyway, add the hardware. Thread
• Louvered motor-pan vent. Bill cut a 4" round hole in the end of the motor pan and covered it with a 4" square louvered, screened vent (half of a 4x8 floor vent). The headstock and motor run cooler, and after years he found no sawdust inside. He made cutting the pan sound near impossible and used an angle grinder on it. Thread
  My version: the hole took about two minutes with a cheap 90mm HSS hole saw and a bit of oil (blade still sharp after). I fitted a 4"/10cm louvered boat vent from the inside for a cleaner look, and left the screen off since the headstock already has its own vent and plenty of other openings.
• Louvered LOGO-cover vent. The same cooling trick at the other end: fit a 4" round louvered, screened cover in place of the LOGO cover on the side of the headstock. Runs cooler and stays free of sawdust, and it's an easy swap over the existing LOGO opening (no cutting the pan). Photo
• Link belt for the motor drive. Replace the moulded rubber A-section motor belt (NOT the Poly-V drive belt) with a 1/2" PowerTwist/Fenner segmented link belt cut to 35 links (~27"). Fit it with the arrow in the drive direction, inner tips folding down as they wrap. Less vibration and noise, and it won't take a set if the machine sits. Bill started on 36 links but they stretched too long in use, so he settled on 35. Non-reversing drives only. Thread
• Single-to-double-bearing quill conversion. Machine the back of a single-bearing quill housing to take a second 35mm bearing (Fafnir 202KDD5), red Loctite on the shaft, for a stiffer, longer-lived quill. Thread. Not being a machinist, I'm going to try a simpler non-Bill version instead: press a needle bearing (IKO BR122016, ~$12) into the outer part of the quill so the rollers ride on the smoothed shaft, no machining. EverettDavis adds a 1-1/4 x 3/4 seal alongside it to keep dust out. Thread
• Steel thread insert for stripped set-screw holes. For rusted-out quill and quill-feed set-screw holes, run a self-tapping steel insert (McMaster-Carr 90259A139) instead of a HeliCoil, so you keep using the normal 5/16" set screws. Thread
• Rust Reformer inside the pan. Spray Rustoleum Rust Reformer inside rusty motor pans and belt covers on every rebuild to stop corrosion coming back. Thread

That's the lot as far as I can tell. Bill was really the only one doing headstock mods systematically, so this is more or less all of it. For the deeper rebuild stuff (rust, paint, motor teardown), ddvann79's restoration index links a stack more threads: 1962 Goldie disassembly / restoration index

If I've got something wrong or missed a mod, sing out and I'll update it.

Here are a few photos of the mods I've done so far:

• Speed control quadrant
• Louvered motor-pan vent
• Rust Reformer inside the belt cover and motor pan

[nuhobby]

Thanks for compiling these... I've got a buddy getting a used Mk 5, and I will refer him here.

[Maurice]

On Facebook where I posted this, I've had a fair bit of push back from people seeing Bill's photo of the link belt in the motor sheaves, citing the wisdom that they'd wear the aluminium sheaves too much and are only good for steel pulleys. Fair concern, so I went digging and pulled together a timeline of everything Bill said about the lower drive belt across his 2,342 posts here.

He'd heard the same warning, and said so up front:

I read that link belts on aluminum pulleys will wear them and was not recommended. I like the idea of no vibration so I switched to link belts in the 90s for my headstocks. I have not seen any noticeable wear on the sheaves but I am sure some wear is beening done.

Drive Belt Quality Concerns, 29 Aug 2008

So he knew going in, and ran them on his own headstocks from the 90s right through to his last post in 2017. He never denied the wear. He argued it's a different kind of wear:

• "the normal V-belt appears to wear grooves in the sheaves whereas the link V-belt leaves a nice smooth finish on the sheaves" (Link PowerTwist V-Belt Question, 21 Aug 2010)
• "I find that the link belt wears more evenly on the sheaves as there is more sheave contact with the link belt" (drive belt radius, 9 Nov 2009)
• "I found the wear on the sheaves over a 2 year period (around 500 hours) with the link belts were about the same amount that I machine off used sheaves (to remove scratches, nicks and mostly worn areas) when I recondition them now" ("But you haven't finished the first one yet", 22 Feb 2012)

He put numbers on the mitigation too. From that same 2012 post: "Blowing out the headstock yearly seems to help keep the aluminum dust problem to a minimum", and elsewhere he says a couple of times a year. Plus, from 2015: "You will need to oil the sheaves more frequently to clean out the aluminum dust if using a link belt" (replacing lower Mark 5 belt with common automotive belt, 30 Apr 2015).

And the caveats, in his own words, which are worth quoting because he volunteered them himself:

• "Yes, the wear of the sheaves on my Shopsmiths was within my limits but I did not use them that often" (same 2015 post as above)
• "I have not done any precision measurements as to how much wear occurs" (same 2009 post as above)

Worth noting what he was actually cutting off used sheaves, and it wasn't link belt damage. From that same 2009 thread:

I find many sheaves with grooves and uneven wear that used the Shopsmith drive belt. I have chucked these sheaves on my metal lathe and recut the face on the sheave so there is a lot of metal that can wear off before there is a problem.

He rejected about 10% of used sheaves outright as too far gone, and that was from decades of standard V-belt use, not link belts.

He didn't land on link belts by default either. He tested the alternatives and dropped them:

• Kevlar - he actually switched his personal headstocks to it in 2010 (the same post as the "smooth finish" quote above), then reversed: "Do not try any Kevlar type V-belts as they are too stiff and really cause excessive noise on the sheaves. I operated a Kevlar V-belt for many hours trying to break it in but the excessive noise and vibration never went away" (Control Sheave Self Destructed, 3 Apr 2013)
• his post-mortem on why, two years later: "The belt overheated (bad smell too) at the SLOW or FAST positions and was a lot more nosier the a standard 1/2 inch V-belt. It did not like the vanes on the sheaves and the short turning circle at each end of the speed range" (same 2015 thread)
• Cogged V-belts (Goodyear AX24, an idea he got from Skip Campbell) - he liked them for vibration and fitted them depending on what the customer wanted (Drive Belt Quality Concerns, 28 Aug 2008), but they never displaced the link belt for him
• Plain automotive V-belts - "I found the auto type V belts do not have a long life when used in the headstock so quickly gave up on them" (same 2015 post as the Kevlar post-mortem)

His last word on it was also his final post on this forum:

I have switched back to using link belts on all my personal reversible Shopsmiths. I like the reduced vibrations and noise in the headstock. I have a few thousand hours using link belts without any problems. The wear on the sheaves were within tolerance for me. I used 36 links on a couple of my Shopsmiths.

Link PowerTwist V-Belt Question, 1 Mar 2017

To be fair to the objection, he knew the rule and repeated it himself as late as 2015: "Link belts should only be used with steel pulleys due to harder wear material in the links." But that sits in the same paragraph as "you will get additional aluminum dust from the wear on the headstock sheaves" and "I have been using the powertwist link belts for more than 30 years". He wasn't unaware of the tradeoff, he just decided it was worth it on his own machines. And he only ever fitted OEM belts to customer machines, with cost as the only reason he gave.

So call me curious. I'll likely only put a few dozen hours a year on my Mark V, which is exactly the case Bill said the link belt suits, since it won't take a set the way a moulded V-belt does when a machine sits. I've also done his louvered vent mod, so there's a lot more airflow through my headstock than most. I'll report back.

[Kent50]

Thank you for posting this!