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!)

517505 517504

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/feds/pdf/Article%20-%20Screw%20Threads%20Design.pdf

[Caleb Crosby]

yes indeed Bill, I actually googled cast iron tear out with grade 8 bolt earlier today and your right at what I found- 5/8. just for the sake of discussion my 'lazy route' shortening a new stud would give me about 1/2" engagement which for a table saw I suspect would be plenty close enough. This Rockwell contractor saw is not very heavy but 2x4's are a good idea. Did I mention the bolt that sheered off was a grade 5. I'm impressed Rockwell used good fasteners - but not good enough!

[Tom Trees]

I had that happen recently, so I drilled a hole, and smushed in a cheapo flathead, i.e one from the very cheapest screwdrivers sets you could buy from the poundshop,
likely ground it a bit, and it worked with no hassle atall.
I was expecting it to be much more difficult, didn't even have to remove the table.
That might be required if you cant get the clearance for the drill.

Saying that, I had been tightening and loosening the bolt prior quite a bit.
517514

Now, if I could only find a nice imperial bolt to replace it with, fat chance of getting anything local.
This lousy bed or couch fixing will have to do for now, and is why I keep onto everything.
I'd probably find it upsetting, if I could see it. :D
517515

Tom

[Jerry Bruette]

yes indeed Bill, I actually googled cast iron tear out with grade 8 bolt earlier today and your right at what I found- 5/8. just for the sake of discussion my 'lazy route' shortening a new stud would give me about 1/2" engagement which for a table saw I suspect would be plenty close enough. This Rockwell contractor saw is not very heavy but 2x4's are a good idea. Did I mention the bolt that sheered off was a grade 5. I'm impressed Rockwell used good fasteners - but not good enough!

Why do you feel that you need grade 8 bolts? It's not like there'll be a lot of pressure on the table top. Can you even reach the torque spec for a grade 8 in the cast iron top without pulling the threads out of the hole? It's not that Rockwell didn't use "good enough" fasteners but that they used adequate fasteners without spending for unneeded expenses. I bet you could hold that table down with ungraded bolts. And if you're worried about vibration squirt some blue locktite on the threads

[John Kananis]

Not much to add a the solutions provided should work. Just wanted to say, hey, that was my very first table saw. And yeah, the fence was frustrating.

The only other thing I'll add, is look into a pals kit to keep your blade aligned to everything properly. GL.

[Caleb Crosby]

Thanks John I'll google that Pals kit. I've used cabinet saws a bit and I know how nice the fences run, but I guess ignorance is bliss I have not used this yet just setting it up - but I really like the lock down and the smoothness - it is 1/32 out of true- the far end kicks in hair But if it stays consistent I can fix it or shim it

[Bill Dufour]

Where is OP located that he can not find an imperial bolt? You might just drill it out and tap to m8 or m10. If you can find a 5/16 set screw...heat it red hot and let it air cool. That should draw the temper so it can be drilled and used as a guide bushing.
If you use a screw extractor use the square non tapered kind. the tapered kind will expand it tighter and make it harder to get out.
Bill D

[Bill Dufour]

For the drill guide bushing a piece of hardwood dowel will work well enough to get a centered hole started. Do you have a lathe or drill press. No lathe? drill the hole first and use a screw and nut as a mandrel to grip in the chuck as you spin it and sand the outer diameter to fit.
Bill D

[Richard Coers]

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/feds/pdf/Article%20-%20Screw%20Threads%20Design.pdf
The part you are forgetting in the equation is the tensile strength of the material. Grey iron tensile strength is quite low. In metric, the ultimate tensile strength of cast iron is 1.3-1.6 tonnes per sq meter, mild steel is 5.5-11.0.

[John Kananis]

The pals kit will fix the misalignment.

https://www.ptreeusa.com/tablesaw_PALS.html


Thanks John I'll google that Pals kit. I've used cabinet saws a bit and I know how nice the fences run, but I guess ignorance is bliss I have not used this yet just setting it up - but I really like the lock down and the smoothness - it is 1/32 out of true- the far end kicks in hair But if it stays consistent I can fix it or shim it

[Caleb Crosby]

Bill, I'm OP but it was someone else looking for that - Mcmaster Carr I'd recco or amazon if no hardware stores around

[Caleb Crosby]

Bill all good approaches - I agree square are the kind of extractor to use - I used to have to extract glued Sony camera screws as a sideline biz and ground my own from HSS 1/4" blanks, get em good and sharp and tap em in before turning sometimes

[Caleb Crosby]

Jerry yes 2 x the diameter in CI with a grade 8 and the bolt will fail first- depending on the grade of the casting. I dont know how age effects CI but I think it gets harder - weird thing is when you drill it out after you get thru the shell (woodpecker hard) its all powder in there!

I want grade 8 bc it will clamp into the threads with more hold before deflecting which I think is more of a problem than failure. and bc I may have to only go in half way with the stuck shaft. Ive decided my first approach is put a 5/8 length bolt in the sheered whole. I'm not trying to make a project here. Just want a tight table. I do have a lathe but cant for the life of me figure out why anyone would use on on this

[Caleb Crosby]

Bill do I have a LATHE!? I have my grandfathers 120 yr old Seneca Falls 9" with a quick change post and all the tooling. He was an MIT engineer and only used it for delicate stuff at home so it's like brand new, can cut to a thou easily. I made a lot of camera parts with it, love the thing. Still driven by the leather belt it "came with" - my father had it on a shelf at his shop for 50 years untouched- too small for any production work

[Caleb Crosby]

I sorta got it - it was a fistfight in a phone booth - got the blade running within 1/100 of miter slot. I picked up one shortie 3/4" long 5/16 bolt for my bum socket and three 1 inch. The shortie hit the jackpot - it fit- so no need to lift the top. Generally with these saws three of the trunnion/table bolts are straight forward easy access but one (Murphy) is right corner, near you facing saw and it's just a smoking crater to get to- up against the wall directly above the tilt control rod- and why in heck are they left hand threaded anyway? Thats some deep baseball there.

Thanks - that PALS look like the thing. I didn't know this was a sort of pervasive/design issue. or maybe they help you keep it in trim bc they are prone to wander? Hope not. if it does I know now where it needs some persuasion to sit straight and I'll add a doo dinger special - bolt a socket to the left rear leg and one to the motor mount rod and connect with some nuts and threaded rod.

Or something like that - thanks for the help and good ideas lads. All this messing around makes the beer go down like a babbling brook!

[Caleb Crosby]

Why do you feel that you need grade 8 bolts? It's not like there'll be a lot of pressure on the table top. Can you even reach the torque spec for a grade 8 in the cast iron top without pulling the threads out of the hole? It's not that Rockwell didn't use "good enough" fasteners but that they used adequate fasteners without spending for unneeded expenses. I bet you could hold that table down with ungraded bolts. And if you're worried about vibration squirt some blue locktite on the threads

I would think Rockwell engineers made good decisions, but all companies have to build to a price as well. I removed 3 grade 5 bolts - prob original - if so- there you go. Seems like the right bolt. But it was a grade 5 that sheered off. the 4th bolt was (probably replaced by a prev owner) - it had no grade marks, the threads were severely deformed (on all 4) but it held up.

[John Kananis]

It's been a real long time but I'm pretty confident my saw didn't have any graded bolts (neither does my unisaw for that matter). Also hard to believe that a grade 5 bolt used in this capacity would shear the head off. Its inherent shear strength is in the thousands of pounds. Imho, you're going way overkill.


I would think Rockwell engineers made good decisions, but all companies have to build to a price as well. I removed 3 grade 5 bolts - prob original - if so- there you go. Seems like the right bolt. But it was a grade 5 that sheered off. the 4th bolt was (probably replaced by a prev owner) - it had no grade marks, the threads were severely deformed (on all 4) but it held up.

[Caleb Crosby]

It's been a real long time but I'm pretty confident my saw didn't have any graded bolts (neither does my unisaw for that matter). Also hard to believe that a grade 5 bolt used in this capacity would shear the head off. Its inherent shear strength is in the thousands of pounds. Imho, you're going way overkill.

It almost sounds like you've got something against overkill. But yeah it's grade 5, it didnt sheer the head, it sheered mid shaft. Like I said above a previous owner could have replaced it- I donno. But other than 5 bucks I dont see any down side to strong fasteners.