Rf-31 Head Bolts Slipping

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Travis7s

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The large 5/8" head bolts on my mill are slipping within their hex shaped cutouts, since its a round column mill this is not very good. The bolts I have are yellow zinc so I suspect the previous owner may have replaced them at some point and the bolt heads are not big enough now. (although the user manual does indeed spec 5/8" as the size.)

Has anyone else had this problem?
 
Can you add a bent up shim (hexagional profile) to make up the difference between the different diameters?
 
That could work, may have to try it. Last night I needed the mill bad so I was using an impact driver to do it :p

A M18 bolt would be just right I think, but tricky to find.

A 3/4" bolt could also work if I bored out the holes a bit, (they measure around .725") and then would probably have to machine the bolt head down to fit.
 
Are the edges of the bolt heads slightly rounded? What grade bolts are they? i'd recommend maybe a grade eight. Just stabbing at it from here.
Andre's shims sound feasible. Good luck.

CHuck the grumpy old guy
 
Look up a thread of mine, mill head bolts. I used all thread with oversized nuts welded on and milled down to fit the recesses in the head casting.


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Last edited:
Thanks mzayd3, somehow I missed that thread in my search. Good info!
 
Andre said:
Can you add a bent up shim (hexagional profile) to make up the difference between the different diameters?
Click to expand...

I also have a round ram and the bolts are solid but not sure what prevent them from turning. let me know if you need me to check for anything. looks like you might have to take that top cover off and see what under there and what holds back the bolts
 
These are mine, just a hex shape is cast into the head, acts like a socket. You can see how much slop there is though and that allows it to slip. I think I will just try to modify 3/4" bolts, does anyone know how hard it is to machine high grade bolts?

JgkcElM.jpg
 
I believe grade 8 bolts will be too hard to machine in most cases. A trip to the bench grinder will probably be just fine, it's not like the hex socket is very accurate to begin with.
 
Grade 8 bolts are <40 Rockwell.
You can machine it with HSS, turns a lot like 41xx

I think you have the right idea to turn down a bigger bolt and put new threads on it.
 
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