shear bolt question

[jellybean]

I have a bomford chisel plough with low draft legs. Shear bolts are 7/16 x 5 inch but they are all rusted in solid so when one breaks I have to drill out 3 pieces. Not easy to keep the holes straight through all 3 pieces so a new bolt will line up all the way through the 3. &/16 bolts are not the easiest to find, neither are the drill bits. 7/16 is 11.11 mm so would an M12 bolt be too tough; cheaper bolts and drill bits?
I don't have oxygen/propane to get the bosses really hot to see if the pieces can be knocked out that way.

 

[Exfarmer]

I have a bomford chisel plough with low draft legs. Shear bolts are 7/16 x 5 inch but they are all rusted in solid so when one breaks I have to drill out 3 pieces. Not easy to keep the holes straight through all 3 pieces so a new bolt will line up all the way through the 3. &/16 bolts are not the easiest to find, neither are the drill bits. 7/16 is 11.11 mm so would an M12 bolt be too tough; cheaper bolts and drill bits?
I don't have oxygen/propane to get the bosses really hot to see if the pieces can be knocked out that way.

These machines always had a penchant for shear bolts.
firstly never use heat it will ruin the temper .
I am surprised you can drill the bolts as they are hard. I suspect you cannot get genuine and are using a softer bolt, which of course means they shear easier.
another reason for difficulty in extraction. is that the faces On the bushes, which do the shearing, have deformed meaning the bolts tend to bend in the shear. This both makes it impossible to knock out and jams the leg.
The ideal answer is to replace the bush, in both leg and frame, but this will cost far more than the cultivator is worth
we ran one from new for several years and in its first year went back to Bomfords to have this very job done. It was a pity as the tool was good for primary cultivation

 

[Lincs Lass]

Any chance of getting the pivot bolt loose to line the sheer holes up

 

[Lincs Lass]

Landlord had a low draft sat in the yard for years ,it got lost in the nettles as the time and cost to make it useable was too much .

 

[Hilly]

I have a bomford chisel plough with low draft legs. Shear bolts are 7/16 x 5 inch but they are all rusted in solid so when one breaks I have to drill out 3 pieces. Not easy to keep the holes straight through all 3 pieces so a new bolt will line up all the way through the 3. &/16 bolts are not the easiest to find, neither are the drill bits. 7/16 is 11.11 mm so would an M12 bolt be too tough; cheaper bolts and drill bits?
I don't have oxygen/propane to get the bosses really hot to see if the pieces can be knocked out that way.
Will they not knock out with a punch and hammer ?

 

[ajcc]

You need to access some gas and heat to remove such bolts. The only solution.imo.

 

[essexpete]

Don't forget the cross section area of the 12mm over the 11.2 is close to 15% larger.
If it were a shear bolt on a baler I would be wary of that. On an old chisel plough I doubt it would be a problem. Softer than spec bolt tend not to shear cleanly but drag and deform.

 

[Exfarmer]

Of course the other issue with these chisel ploughs rain water went down the legs and could not escape. This would then freeze in a hard frost and swell the legs , splitting them and exposing the non wearing parts to wear as the shear no longer covered it.
great shame as thought it was the bees knees when they first came out

 

[Pennine Ploughing]

If it were me, and have had this problem in the past, as @Exfarmer says the bushing can get deformed and bend the bolt, rather than shear it clean, a bent bolt is hard to get out,
I would drill the holes out to 14 mm, and fit 14 mm bolts, measure the leg and bushing up correctly so you can find where the joins are on the length of the bolt,
then get someone with a Lathe to put a narrow grove with a "parting tool" 1.4 mm deep, this will be nothing of a job to a lathe man,
this should end up looking like a bolt with 2 shallow groves where it is meant to shear,
same spec of bolt only bigger on lands to ensure a clean break on pressure point
on doing this bush faces should be should be square, and a clean shear on the bolt, but must be tight for a clean break,

and ease of removal with a good drift and big hammer, bad drifts and small hammers are no good,

 

[jellybean]

So one person says heat them up, another says don't! I can get the legs to swing from the pivot bolt so it is kind of possible to line everything up to drill out old bolts but that means going through 4inches of metal. Obviously keeping the drill absolutely straight while going through 3 pieces of shear bolt is virtually impossible but I have done 2 so far. Even taking the leg off and getting it under the pillar drill is not much better.
I have some M12 bolts here, some are solid shank, some are all threaded. I am guessing that if I put in the threaded ones their shear point wouldn't be much different to the original 7/16 bolts, possibly even weaker, in which case I could put in the solid shank bolts. No amount of hammering will get them out, even after drilling a hole through.
I would love to have good gas heat but the sets are not cheap.

 

[Pennine Ploughing]

bolts have their threads rolled on to them, this reduces the diameter so wont be a snug fit, and while rolling the threads on it distorts the properties of the steel, and makes them weaker

 

[bobk]

Has it got depth wheels ?

 

[jellybean]

Has it got depth wheels ?

Yes it has and I am only going about 6 inches deep. Problem was a buried stump at the bottom of a slope that I have been clearing. apart from that it's doing a great job and very happy with it.
I will get it fixed, what else are bank holidays for?

 

[Barleymow]

I carry a hacksaw blade only take short time to cut bolts so can punch out

 

[Tim Howard]

All the chisel ploughs I have seen have a clamp over the frame with 2 or 4 bolts holding the leg to the frame
The Shakarater uses these as shear bolts, would it be possible to weld the leg up around the shear bolt and fit a smaller bolts threw the cap.

 

[Fivedoors]

I have a bomford chisel plough with low draft legs. Shear bolts are 7/16 x 5 inch but they are all rusted in solid so when one breaks I have to drill out 3 pieces. Not easy to keep the holes straight through all 3 pieces so a new bolt will line up all the way through the 3. &/16 bolts are not the easiest to find, neither are the drill bits. 7/16 is 11.11 mm so would an M12 bolt be too tough; cheaper bolts and drill bits?
I don't have oxygen/propane to get the bosses really hot to see if the pieces can be knocked out that way.

Have the very same problems especially drilling them out using a low speed drill which when catches turns your arms as part of the drill body [emoji50]the bolts I know use are cup or cap heads Allen key slightly thicker than the originals and also longer I just sand them a little nearer the hole size which is usually egg shaped grease them well and drive them in ,luckily none have broke so removal might be a challenge