Got to shorten the thread on 320 shoulder bolts what's the most efficient way?

[Bki26]

Was originally thinking of sticking a bit of bar in the lathe and parting it off until it's the same thickness as the required thread length then tapping it so I can set each bolt before parting off and the action of removing it would reform the thread where it's parted however that method might be awkward as I'll have to get the bolt in through the spindle bore and I don't think I have a allen key long enough, requires running in reverse with the tool upside-down or at the back and the thread is 9.5mm long but I only want 5mm so very little surface for the 3 jaw to grab.

My other idea was to hold the shoulder bolt in the 3 jaw and use the head to index off the back side of the jaws which would let me run it normally but I've never managed to cut down a thread on the lathe without destroying it and thus always had to put a nut on beforehand to reform once cut. The only way I think I could make this method work is the use a 30° insert as a parting tool since it'll also chamfer the edge when plunging it in?

 

[voipio]

How big a bolt, and how much of the threaded part needs to be removed?

 

[Wildefalcon]

And how much would the correct bolts cost?

 

[Agroshield]

Put some washers under the head and against the shoulder so the end of the existing thread ends up in the correct place.

Neater variations on this theme (like a threaded spacer the same OD as the shoulder) are possible.

It makes sense to design a product you are trying to sell commercially to use standard hardware.

 

[Bki26]

How big a bolt, and how much of the threaded part needs to be removed?

As said thread section is ~9.5mm I need it at 5mm, the whole shoulder bolt is d6x12mm m5 thread.

And how much would the correct bolts cost?

That's the best bit, they don't exist hence need to shorten the thread of the existing ones with the required shoulder dimensions I ordered.

 

[Erie Fred]

Does your lathe handle 5-c or other collets ?

 

[Gareth J]

Have a cold saw or abrasive chop saw? For that many, I'd spend 1/2hr on a jig that would let me clamp the bolts in place, repeatably, with a nut on them, saw 5mm off, wind the nut off and repeat.

If there's space, before removing the nut, running the bolt in a cordless drill against a bench grinder will remove burrs and lightly chamfer

 

[Dapph2]

Drill a hole in some 5mm thick flat bar stick it in a vice , hand hold the bolt in it and use a thin cut off blade in an angle grinder to follow it to cut to the threads length, use a fine triangular file to clean up the thread and make a good lead in .

 

[Agroshield]

Don't use a shoulder bolt. Use a variation on this:

https://www.decathlon.co.uk/p/front-and-rear-wheel-axle-kit-for-play5-scooters/

I believe they are called Chicago bolts

Use a 6mm OD sleeve of the correct length with a female thread both ends. Loctite in a piece of allthread one end and a socket capscrew the other end (M4 rather than the M5 of the item pictured or the wall will be too thin).

 

[Bki26]

Don't use a shoulder bolt. Use a variation on this:

I'm using a shoulder bolt because I need a shoulder bolt and the parts have been made for a shoulder bolt and that method just isn't practical for the application.

Have a cold saw or abrasive chop saw? For that many, I'd spend 1/2hr on a jig that would let me clamp the bolts in place, repeatably, with a nut on them, saw 5mm off, wind the nut off and repeat

Only a grinder hence lathe as wouldn't take long cutting down 320 m5 threads compared to the 1200+ thumb screws I did recently.

 

[Morrisman]

Make a split collar out of round bar, with a shoulder that will act as a stop against the chuck jaws. Make it suitable length so the right amount of the bolt protrudes out the front. Grip each bolt, part off and chamfer the thread.

 

[julianf]

If great accuracy wasnt an issue, i think i would drill and tap a load of holes in a bit of steel, screw a bunch in, and have at it with a slitting disc, and then a flap disc.

Your thread would get a little shorter with each batch, as your flap disc would wear the jig a bit, but, depending on material, care, etc not much at all.


I used to do potentiometer shafts like this, but not in the same numbers.

 

[Bki26]

Make a split collar out of round bar, with a shoulder that will act as a stop against the chuck jaws. Make it suitable length so the right amount of the bolt protrudes out the front. Grip each bolt, part off and chamfer the thread.

Decided to do something along those lines, excuse the bad drawing but gonna make a short bar with a lip to register against the jaws that the shoulder bolt screws into and I'll cut the face down till the right amount of threads is sticking out so all I have to do is screw one in, clamp the lot in the 3 jaw, part it off and unscrew which would fix the threads post cut before repeating.

 

[Screwdriver]

Run a nut onto it the right thickness to leave the required amount of thread exposed.
Trim that off with an angle grinder either with a cut off disk or a flap wheel.
Use a chamfer cutter to tidy up the end.

 

[Agroshield]

I'm using a shoulder bolt because I need a shoulder bolt and the parts have been made for a shoulder bolt

The parts have not been made for a _standard_ shoulder bolt, hence your requirement for modifying the items.

It may be more economic for your Mark II model to research standard available industrial fasteners and design around them.

It would also be worth submitting a drawing of the item you currently want to one of the overseas manufacturing concerns. At a piece count of 320, you might be surprised at the price - the hex socket would probably add to the cost, so an alternative head style (hexagon or round/domed and slotted) could reduce that.

 

[wyn]

Decided to do something along those lines, excuse the bad drawing but gonna make a short bar with a lip to register against the jaws that the shoulder bolt screws into and I'll cut the face down till the right amount of threads is sticking out so all I have to do is screw one in, clamp the lot in the 3 jaw, part it off and unscrew which would fix the threads post cut before repeating.

Will the lathe tool just unscrew it as soon as it touches or will the holding thingy be split to exert some clamping force?

 

[julianf]

What about a mushroom shaped thing -

Flat round plate as the cap of the mushroom, tapped for job, in a circle, close ish to its edge.

Then this is welded to the "stalk" of the mushroom, and it's the stalk that you hold on the lathe.

This means you can easily get to both sides of the mushrooms cap (the flat plate with all the screws screwed into it) for loading / unloading, and you could spin it up and turn off all the threads at the same time.

Construction time for the mushroom would be minimal - weld it up rather than turn it from a solid lump. Loading and unloading would be quick. Doing the cutting would be nicer and more precise than the grinder method.

 

[bricol]

The parts have not been made for a _standard_ shoulder bolt, hence your requirement for modifying the items.

It may be more economic for your Mark II model to research standard available industrial fasteners and design around them.

It would also be worth submitting a drawing of the item you currently want to one of the overseas manufacturing concerns. At a piece count of 320, you might be surprised at the price - the hex socket would probably add to the cost, so an alternative head style (hexagon or round/domed and slotted) could reduce that.

Plenty of British companies too - I was surprised at a quote I got a couple years ago for captive screws - we were paying something silly, pounds per screw from a local engineering company. From a fastener company, they were pence. If I remember, I'll look them up at work tomorrow.

I dislike using bespoke fasteners, or even weird size standard ones - 'cos you know when one breaks out in the field somewhere, you aren't going to be able to get a replacement from the supplier down the road.

 

[Guzrik]

Mount them all into their definitive product and position and then cut them flush with angle grinder. Done?

 

[Morrisman]

Decided to do something along those lines, excuse the bad drawing but gonna make a short bar with a lip to register against the jaws that the shoulder bolt screws into and I'll cut the face down till the right amount of threads is sticking out so all I have to do is screw one in, clamp the lot in the 3 jaw, part it off and unscrew which would fix the threads post cut before repeating.

View attachment 504519

You don’t need to screw anything in, just cut the collet in two so it clamps the bolt when you tighten it in the chuck. Have the thread poking out far enough that you can part it off and chamfer it.