What are you machining?

[fizzy]

Modify a BT40 holder to Int40
M16 thread which I needed to drill out to fit an extension piece.
Very hard steel so HSS won't touch it. Carbide boring bar but slow.
If only I had a bigger solid carbide end mill but they are silly money.
Despite having so many lathes it's always my trusty old Colchester Triumph roundhead I turn to.
Adapter held in with special heat setting epoxy. 6000psi strength and 5.5 sq inches so shouldn't pull out. Too hard to drill to pin. Working fine.

 

[Johnnybravo]

Modify a BT40 holder to Int40
M16 thread which I needed to drill out to fit an extension piece.
Very hard steel so HSS won't touch it. Carbide boring bar but slow.
If only I had a bigger solid carbide end mill but they are silly money.
Despite having so many lathes it's always my trusty old Colchester Triumph roundhead I turn to.
Adapter held in with special heat setting epoxy. 6000psi strength and 5.5 sq inches so shouldn't pull out. Too hard to drill to pin. Working fine.

View attachment 438875

View attachment 438876

If it does pull out you have a serious headache on your hands.
No need to modify the holder. You can make, or buy adapters that screw in

 

[Johnnybravo]

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[fizzy]

If it does pull out you have a serious headache on your hands.
No need to modify the holder. You can make, or buy adapters that screw in

How can you have M16 in both? Unless I am not thinking it through properly. Surely if you drill a hole deep and tap it M16 there would be nothing left of the threaded bit at the bottom? My drawbar is very long sadly and too much hassle to remove the whole air assembly.
I have left a small amount of thread at the bottom as a backup. just in case.
The epoxy I have used is awesome stuff. Never seen anyone using it before.
Heat curing. Single pack. Flows like solder. You bake it in an oven at 170C for 45 minutes or so. Much stronger than 2 part epoxies. Not cheap and has to be stored in a fridge.

 

[Johnnybravo]

How can you have M16 in both? Unless I am not thinking it through properly. Surely if you drill a hole deep and tap it M16 there would be nothing left of the threaded bit at the bottom? My drawbar is very long sadly and too much hassle to remove the whole air assembly.
I have left a small amount of thread at the bottom as a backup. just in case.
The epoxy I have used is awesome stuff. Never seen anyone using it before.
Heat curing. Single pack. Flows like solder. You bake it in an oven at 170C for 45 minutes or so. Much stronger than 2 part epoxies. Not cheap and has to be stored in a fridge.

Don’t drill the hole too deep. It’s a blind hole,not a through hole.Buy one from pro tool and copy the dimensions. You can make them a lot simpler. They don’t need the wasted down section or the flats.

 

[Hood]

I made a load up years ago for a friend to use on his mill, don't have a pic of them but do still have the 3D model.

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Also did similar for my Beaver mill pull studs, pic on right is standard pull stud I made, one on left is the extended pull stud to convert BT and CAT holders.

 

[Hood]

Cross section of ones I made for my friend.

 

[fizzy]

Don’t drill the hole too deep. It’s a blind hole,not a through hole.Buy one from pro tool and copy the dimensions. You can make them a lot simpler. They don’t need the wasted down section or the flats.

That's basically what I did. On the next one I will try leaving the bottom thread a bit longer.

 

[Munkul]

My drawbar is very long sadly and too much hassle to remove the whole air assembly.

I have the same issue meaning I can't use those adapters either. It's not a massive amount of hassle to remove the drawbar - I assume it's similar to mine with a couple of spring rods to remove the impact gun from on top...

I never bothered because I only have 1 or two BT40 toolholders and they were cheap....

 

[fizzy]

Cross section of ones I made for my friend.

View attachment 438913

Sadly my drawbar is much too long for the inch or so of the top bit.
I need it about half an inch longer again into the bottom but will leave a bit more thread down there next time. Even a few turns should be strong enough.

 

[fizzy]

I have the same issue meaning I can't use those adapters either. It's not a massive amount of hassle to remove the drawbar - I assume it's similar to mine with a couple of spring rods to remove the impact gun from on top...

I never bothered because I only have 1 or two BT40 toolholders and they were cheap....

I did think about it but I only have 3 of these holders which I had dirt cheap on Ebay - they are nice quality ER32 so didn't want to waste them.

 

[Kram]

Very hard steel so HSS won't touch it. Carbide boring bar but slow.
If only I had a bigger solid carbide end mill but they are silly money.

Boring bar is correct choice why would you use an endmill for it?

 

[Johnnybravo]

Sadly my drawbar is much too long for the inch or so of the top bit.
I need it about half an inch longer again into the bottom but will leave a bit more thread down there next time. Even a few turns should be strong enough.

Shorten your drawbar or machine a bronze spacer to go underneath the head of the drawbar. These are a standard item and have worked on at least 6 different 40INT machines I have used over the years. So something amiss with your draw bar.Could be something missing ie a spacer. Or two spacers, one under the drawbar head and one under the tool changer. I would sort it out as it’s a lot easier and cheaper to use bt40 toolholders.

 

[Hood]

Sadly my drawbar is much too long for the inch or so of the top bit.
I need it about half an inch longer again into the bottom but will leave a bit more thread down there next time. Even a few turns should be strong enough.

That is way too much thread, all it is doing is wasting air and time screwing it in and out. I would cut it as you never know when cheap BT or CAT holders will pop up, can never have enough holders and when I was using the Beaver I found I could have done with more than this.

Same with the Chiron, I have these but always could do with more.

 

[fizzy]

You are both right. The drawbar takes and age to screw in and out. Definitely no need to be so long

 

[fizzy]

Boring bar is correct choice why would you use an endmill for it?

I have a 16mm carbide end mill. It removed some of the thread like a hot knife through butter. The 2 boring bars I tried were on their limit. Screaming like banshees. Much easier when some of the thread was removed. I reckon 10 seconds work with a 20mm end mill.

 

[Kram]

Then something is wrong with your boring bar or the insert worn, or wrong type for the job. The screw does not look original, correct countersink angle?

 

[Munkul]

I thought the same thing too, NGL that boring bar looks clapped fam

 

[fizzy]

Then something is wrong with your boring bar or the insert worn, or wrong type for the job. The screw does not look original, correct countersink angle?

I tried the new one it was even worse. Brand new insert. This steel is seriously hard stuff. HSS doesn't even make a mark.
The fact it is a screw thread in there doesn't help either.

 

[Kram]

I can turn hard steel with no problems, the inserts I use are unavailable now or I would recommend them. I'll admit its not easy to find a good insert for boring and hard steel complicates that a bit more.
Suggest a light finishing or stainless grade of carbide insert for boring. If it is really hard then the CBN inserts come out - but generally most items with a thread can be turned with carbide.