Topic: Inside thread repair using 4140 steel:can it be tapped with a standard tap ?

[grcamna2]

I have an inside thread repair to do to a small Honda with a removable right footpeg.
I have drilled and tapped this particular Honda mild steel footpeg bar a few times since 2016',starting from the stock 8x1.25mm;now it's almost to 1/2" size:soft stuff and the threads don't last long.
I want to repair it by installing a 1" long piece of 4140 1/2" round bar into the center of the footpeg bar and having a welder tig my cut-off piece of it on both ends,then weld it back onto the footpeg bar;this 4140 is much harder and the threads will last.
Do you think I'll have a problem drilling & tapping this 4140 round bar out to 8x1.25mm inner threads using HSS drill bits and a standard 'homeowner' Craftsman tap ?

[simon#42]

you should be fine , there is a risk of the tap breaking but if you take your time and use a good tapping lube you will be ok .  not sure about the quality of your tap though , if you have any doubt about its quality buy a better one .

[flatlander]

if you tap the 4140 bar first, before welding it in, there's no damage done in case it doesn't work out (except maybe to your tap).
but i agree, it should work out. back the tap out frequently and keep adding lube.

[calj737]

This is a terrible idea. The stock hole is now 1/2” and the stock stud is 8mm. That means the wall thickness of new round bar will only be 2mm thick. You are not likely to get the new hole concentric unless you use a drill press (minimum) or use a lathe.

You don’t need to weld the new “sleeve” if it’s round bar. Just thread is externally to match the current threads and Red LocTite it in. And do the same to the stock stud to help prevent movement of the peg which is why it’s needing constant repair.

And “No”, your cheap Craftsman taps won’t cut 4140 round bar worth a sh!t.

[RAFster122s]

Why not source a new footpeg bar for this bike rather than the expense of trying to fix this yet again?
Unless this is welded to the frame why not throw in the towel on this right footpeg to replace it with one that isn't failing on you frequently it sounds like this one is doing just that...

[grcamna2]

you should be fine , there is a risk of the tap breaking but if you take your time and use a good tapping lube you will be ok .  not sure about the quality of your tap though , if you have any doubt about its quality buy a better one .

Simon,I was reading online about this;a couple machinists forums said they used a quality tap and someone mentioned HSS drills and taps.
What type is a high quality tap to use ?

[grcamna2]

This is a terrible idea. The stock hole is now 1/2” and the stock stud is 8mm. That means the wall thickness of new round bar will only be 2mm thick. You are not likely to get the new hole concentric unless you use a drill press (minimum) or use a lathe.

You don’t need to weld the new “sleeve” if it’s round bar. Just thread is externally to match the current threads and Red LocTite it in. And do the same to the stock stud to help prevent movement of the peg which is why it’s needing constant repair.

And “No”, your cheap Craftsman taps won’t cut 4140 round bar worth a sh!t.

I'm considering having a machine shop do the threading on a lathe.

[grcamna2]

Why not source a new footpeg bar for this bike rather than the expense of trying to fix this yet again?
Unless this is welded to the frame why not throw in the towel on this right footpeg to replace it with one that isn't failing on you frequently it sounds like this one is doing just that...

The bike is 41 years old:new footpeg bars are no longer available,plus these mild steel threads were a weak design from the beginning because I feel it needed an insert from the factory.
David,try to be a bit more encouraging;it'll change your own outlook in life.

[flatlander]

are there any timesert or bigsert type thread repair things that would fit? that would save you the hassle of making your own.

[grcamna2]

are there any timesert or bigsert type thread repair things that would fit? that would save you the hassle of making your own.

Yes,I had that checked & measured at a place that installs Timesert inserts.
The threads that are in there now are just a little larger than optimum for a proper fit of a 12mm Timesert,which is the largest one possible to install into the hollow bar.
I will be going ahead with a piece of 4140 round bar and doing this intended project. thanks 

[grcamna2]

The question of this thread is:what's a very good quality/brand tap to purchase to cut new threads into 4140 steel. ok?

[BomberMann650]

I don't know about brands for taps.

But i've been steadily converting much of my hole-making tools to carbide.
Or its little cousin Cobalt.

Not that i run up against super hard metals often.  But when I do.  Carbide makes the job easy.

Might be able to find single tap in the size you want.  Rather than buying a whole set.

[calj737]

I’d be astonished if the foot peg is actually steel and not some mystery cast alloy. That would explain why the peg threads continue to wallow out. So if the peg is indeed cast aluminum, nobody can weld 4140 to it.

Your machine shop will have to thread the OD to screw into the existing hole, then internally thread the plug to fit the peg stud. Expect to pay $100 minimum for their time and labor.

I’d love to see an actual picture of this setup.

[flatlander]

I'm considering having a machine shop do the threading on a lathe.

that makes sense considering the precision that will be needed. then they'd be using their own tap which i presume would be higher quality than a cheap amateur piece, and if they know what they're doing they'd make the right choice for the material. so why are you shopping for a tap, then?

to the inserts: timesert makes a huge selection of sizes, and there are other makes that offer all sorts of dimensions. i'd be surprised if there wasn't one available that fits. it would make the whole operation easier than fabricating your own.

[grcamna2]

I'm considering having a machine shop do the threading on a lathe.

that makes sense considering the precision that will be needed. then they'd be using their own tap which i presume would be higher quality than a cheap amateur piece, and if they know what they're doing they'd make the right choice for the material. so why are you shopping for a tap, then?

to the inserts: timesert makes a huge selection of sizes, and there are other makes that offer all sorts of dimensions. i'd be surprised if there wasn't one available that fits. it would make the whole operation easier than fabricating your own.

Thank you flatlander 

[simon#42]

not sure about american makes of taps so cant really recomend one . i think flatlanders idea is the way to go i have used timeserts for years and they make for a good repair  .

[grcamna2]

I called a nice machine shop in Woodland and they quoted a price to me which I just can't refuse;they also have the 4140 in house.
I have used and depended on Timeserts in the past and they are 'top of the line',although my original(damaged)footpeg bar/tube has already been threaded inside just a hair too big to have a 12mm Timesert installed into it for an effective repair.

I verbally contracted with the machine shop today and he will drill and thread the 1" piece of 1/2" 4140 round bar by the end of the day.
 I'm going to squarely cut 1.25" off the damaged end of my orig. footpeg bar/tube,then I'll install that custom 1" piece of 4140 1/2" O.D. round bar 'insert' into that 1.25" piece of footpeg bar after tapering each end of the 'insert' on a grinder in preparation for it to be welded inside the piece of original footpeg bar/tube and then I'll take it to my welder who will carefully/lightly tig weld(wooden dowel inside the center threads to protect them while being tig welded)each end prior to welding the 1.25" piece of repaired footpeg bar back on,all trued-up and marked for position.

I also have this spare/custom footpeg bar for the small Honda which I had a pair of CL350 footpegs/bar mounts with hinge,these were installed by a welder a while back;I'll run them on the small bike until this repair is accomplished.
I'm still running the original footpeg bar(which needs this repair)on the bike now;the offending right peg bolt is not able to be correctly torqued on it's mount which bothers me,hence the need for repair.
These custom(pictured)footpegs are fine to run full time,only the pegs sit-up about an inch taller than the originals.
That project was quite a learning model to educate me on making sure the footpegs sit in the proper position/alignment with the correct orientation on the bike;these custom ones will work ok in the trails or with a rider that has shorter legs.

These are pics of the 'used off Ebay' custom 81' CB125S footpeg bar which I modified using both CL350 twin footpegs with short bar and hinge assembly.My original footpegs are of similar bolt-on design on the right peg which allows the clutch cover to be removed while keeping the bar attached to the engine,separately removing that right peg.My original footpeg bar does not have the folding feature;just a one-piece bar and I wanted a better option.I set-up a much stronger piece on the right peg inside the bar and threaded it,had a welder install that threaded piece then quenched it for a bit more hardness:it's good.

[simon#42]

now i have seen what you are doing i would weld a bar in that was threaded at the end and put a nut on it .

[flatlander]

yes that makes sense.

[grcamna2]

now i have seen what you are doing i would weld a bar in that was threaded at the end and put a nut on it .

Ok,I'll consider that idea.

[Kelly E]

I like Simon's idea, quick, easy and it won't look out of place.

[Don R]

 Whatever you try, avoid drilling and tapping weld material. I welded up holes in 4130 to move them a half hole diameter, drilling them back out was nearly impossible.