Old Rockwell 10 tablesaw- trunion bolt sheered off in table

[Caleb Crosby]

Hello everybody, my first post here, been reading for a long time. Gearing up to make some replicas of a coffee table my dad made in 1954.

Bought a table saw and jointer and have been overhauling and tuning them - scraping a lot of rust but at $100 each they are both champs -running strong and quiet. Picking up a 15" Taiwanese AMT planer Friday ($200). I'm basically losing it buying all this stuff. I have a little 700 sq/ft machine shop with zero room for any of this so they will live on castors in wood shed and under carport for operation. (takes care of dust evac!)

Screen Shot 2024-03-25 at 7.25.59 PM.jpg Screen Shot 2024-03-25 at 7.25.38 PM.jpg

So I noticed my blade was not square to my table by 1/16 and started in on that today - ended up sheering one very old 5/16 bolt. About 1/2" of the tip is lodged all the way up in the socket.

I don't want to extract that sheered stud - plan to get 4 new grade 8 bolts tomorrow, cut one short so it will have an air gap and snug it under the broken one with probably 4-6 threads biting, some blue lock tite to help it stick.

Thought it might be smart to run this plan by you guys to see if I'm missing something. With three good studs and the 4th in there a bit I don't foresee a problem - but Ive been known to miss a thing or two or atleast that's what my girl says ;-)

thanks Caleb
New Orleans

[Tom M King]

I would want to get the broken piece out. Left handed cobalt drill bit, or at worst drill it out and upsize to 3/8” at worst.

I’ve bought sets of three taps off eBay used and all have been useable.

5/16 is pretty small. Might have to grind it flat to get a good starting point for the left handed drill bit.

Soak overnight with Blue Creeper or some such

[Bill Dufour]

I would use a F drill to put a dimple in the center of the old bolt. F is the tap drill for 5/16 thread. Actually ,since I have a lathe, I would drill a 1/8" hole down a 5/16 bolt. Then screw that bolt into the hole and drill the lower bolt out at 1/8". then I would drill the guide with a drill just under F size and drill out the old bolt. Then try to pick out the threads. Go up to a F drill if needed.
Any reason not to drill all the way through and leave a F drill size hole in the tabletop?
Bill D

[Tom M King]

The brass threaded inserts are good things to make into drill guides for such things.

[Caleb Crosby]

"I would want to get the broken piece out." TOM

You're right, I should atleast give it a whack - might get lucky. I have lefty bits and extractors but the location it's in is why I prob gonna give up on it. I just spent a couple days getting it all together and the bolt is in very cramped quarters - no way of doing any clean work with a hand drill. What happens if I just release all 4 trunnion bolts? Can I lift table clean off? Seems too good to be true. But if so I can put it on my mill table and back that bolt out in a couple mins- nothing like running a mill backwards with a sharp bit to make a shaft obedient. Just worried about the trunnion getting out of true in some new way that gets slippery.

[Caleb Crosby]

I'm trying to understand what your saying. I have a lathe but I don't see how to bring it to bear - I can maybe dimple the broken shaft with a transfer punch - but there is no drilling in there, no swinging a hammer either - can only get a socket on it mostly by feel- blind - but with a little flashlight thru the curved cut out for the tilt wheel. I think it's either remove table (which Ive never done but might work) or stick with my original plan of an air gap - new shorter bolt. I'm all for using the lathe tho!

[Caleb Crosby]

"The brass threaded inserts are good things to make into drill guides for such things."

that's a really good idea, but again it's up against the wall behind an arm and a loaded bear trap - I gotta use an 18" extension to even get a socket on it. it's remove table or go with my lazy plan A

[Richard Coers]

Remove the other 3 bolts and take the table off the base. Now you can do it right. 4 threads will not hold the proper tightening torque.

[Caleb Crosby]

Easily done - Thanks Richard. I was not sure if I could just lift it off. Yes will def feel better with it removed. Just to play devil's advocate tho - the first engaged thread holds something like 90% of the load, exponentially down from there with each successive thread. 4 threads especially with a grade 8 bolt would be whisper close to nominal spec. But I'm with you - hard to argue against doing things the right way when you can !

[Mark Gibney]

The fence on your saw is not one I enjoyed using years back. As far as I remember it tightens against the round rail on both ends of the table, and was impossible to keep square.

[Caleb Crosby]

yes that's the one - a "Jet Lock" If you saw what I'm used to using (crappy little box store Skill) this fence is a new dispensation. I've cleaned and oiled it, made initial adjusts and it's within a 1/32 which is not good enough agreed, but it's solid, slides well and locks down well. I might cut a long piece of nylon or PTFE and connect with a fine thread to create an adjustable offset if I can't get it true. If I can get it true I'll prob just wax it - really want it to be more slippery.

[Caleb Crosby]

Mark just curious what kind of saw are you using now that has a good fence ?

[Richard Coers]

You didn't mention you were a mechanical engineer. One thread will not hold 90% of the load. It's very easy to pull out one thread in grey iron. I learned that working on farm machinery, not college.

[Bill Dufour]

Standard rule of thumb is 1.5 times the bolt major diameter for a good threaded nut thickness in steel. Cast iron I would want to see at least 2x diameter so 10/16" or 5/8" of good thread in cast iron.
Unisaw and Rockwell 12/14 is four bolts hold table top to the cabinet. Easy to remove. Watch out for any shims/spacers and which corner they go to. Unisaw top is about 100 pounds without wings. Engine hoist and sling through the saw opening is easy job.
Couple of 2x4s at an angle make sliding top back up easy enough. Make sure cabinet is not going to roll away as you push
BilL D

[Caleb Crosby]

One full thread is not easy to pull out in fact bolts are specially designed so the first thread does not carry 100% of the load. From Fastenal:

"This is designed to yield the nut threads to ensure the load is notcarried solely by the first thread. As the thread yields, the load isfurther distributed to the next five threads. Even with the loaddistribution, the first engaged thread still takes the majority ofthe load. In a typical 7/8-9 Grade 8 nut, the first engagedthread carries 34% of the load."

Other calculations for different applications can place the first thread up around 90%. But heck I wasn't trying to argue, more like confess my lazy thoughts. I am no engineer, I work with machining and enjoy reading and researching all kinds of crazy stuff. It's surprising info about threads - it surprised me . Three threads is used by some old engineers as a rule of thumb for max holding power - but depth (more threads) are still needed for accumulated stresses like vibration over time.

I just think its good to know this stuff bc it's counter intuitive and it helps you make decisions. Thanks again for the green light on lifting the table off. I didn't know.

https://www.fastenal.com/content/fed...s%20Design.pdf