Threads on 10mm SS bolts

[Ian_Edwards]

I want to extend the threaded part, on 4 @ 10mm SS bolts by about 5mm.
I have the correct size of die, but the bolts look like they have been stamped, so they don't have machine cut thread.
Before I have go at this, I wondering if the SS will have been work hardened by the stamping process, and it'll be very difficult to cut the extra few mm of thread I need.
I don't want to use set screws, the application is a shaft coupling, and I think it is better to have bar inside the flange.
Any thoughts on how practical it'll be to cut the extra threads?

 

[DownWest]

Washers? Bit easier than thread cutting (those are rolled threads) if you have the room for the length of bolt. Likely you can cut the threads, but not as strong as the rolled original.

 

[Plum]

I want to extend the threaded part, on 4 @ 10mm SS bolts by about 5mm.
I have the correct size of die, but the bolts look like they have been stamped, so they don't have machine cut thread.
Before I have go at this, I wondering if the SS will have been work hardened by the stamping process, and it'll be very difficult to cut the extra few mm of thread I need.
I don't want to use set screws, the application is a shaft coupling, and I think it is better to have bar inside the flange.
Any thoughts on how practical it'll be to cut the extra threads?

The threads will have been rolled, not stamped, but provided you have good quality dies and use a lubricant it will be ok. Did the coupling manufacturer specify what grade of bolts to use? They would usually be specified as high tensile not stainless.

Edit: also, the torque is transmitted through the coupling by the friction of the two flanges clamped together. The bolts are not a tight fit in the holes so if the bolt shanks were transmitting the torque the two flanges would slide one way then the other when you went from forwards to reverse. The bolts are there purely to provide the clamp load. Therefore there is no requirement to have a smooth part of the shank in the holes so set screws will be fine. Clamp load is essential, applied by the correct tightening torque of the screws which is why they would usually be high tensite screws.

Www.solocoastalsailing.co.uk

 

[vyv_cox]

300 series bolts come in three strengths. Unmarked they are 50, if marked on the heads they will be A70 or A80. None of these can really be described as 'High tensile', just stronger than annealed. They will cut easily.

However, rolled threads have far better fatigue resistance than cut ones, so make sure the cutting is done as well as possible and if you can, smooth the roots off with abrasive papers.

 

[NormanS]

Is it not the case that the body of a rolled thread bolt is actually smaller than the thread size? If so, it won't be feasible to cut proper threads with a die. There simply will not be adequate material. Anyway, as has been said, the bolts are merely holding the faces of the two couplings tightly together.

 

[C08]

Good luck with it-I have found threading stainless very difficult but perhaps because I have used cheap dies.

 

[Ian_Edwards]

Thanks all, I'll revert to plane B and use set screws, I hadn't appreciated that friction did the work, and the bolts need to be in tension to make the coupling work. I was thinking the bolts will be in shear

 

[Rum Run]

I'd use carbon steel bolts marked 8.8 as a minimum, and slap some grease on them . Inspect annually and replace if there is excessive corrosion. But there won't be excessive corrosion unless there is salt water splashing about, which hopefully there isn't.
What do the coupling manufacturers say? Unless they specify SS fasteners I would not go there.

 

[penfold]

I'd use carbon steel bolts marked 8.8 as a minimum, and slap some grease on them . Inspect annually and replace if there is excessive corrosion. But there won't be excessive corrosion unless there is salt water splashing about, which hopefully there isn't.
What do the coupling manufacturers say? Unless they specify SS fasteners I would not go there.

What he said; unless the maker specified stainless replace with 8.8 or better still 10.9 of the correct length.