Taper reaming a hardened steel shaft?

So we need to change a straight pin to a taper pin. The original hole was ~.125. The taper pin hole is ~.138 on the small side to ~.153 on the large end. The collar was aluminum but the shaft is a very hard steel (I will measure the hardness when I get it back.) Ordered a carbide #0 taper reamer with a pilot to let the original hole be the guide. Tapered reamer broke. This was being drilled with a cordless drill. This is going to be an occasional thing so efficiency isn't critical.

So my questions are:

1.) I can get a tapered #0 reamer from MSC quick, but it will be HSS. Will it be able to finish the job?
2.) What's the best process to go from the original .125 hole to the taper hole? Drill to #30 (.1285), Drill midpoint to #26 (.147)?
3.) What are the right speeds/feeds?
4.) Do we need a rigid setup in a V-block on a mill, or go in the other direction with a T-handle and no power?

I'm a moderately experienced engineer, though machine shop operations are not my knowledge base. This is being done by a machinist who is experienced, but taper reaming is not a common operation for us.

I'll post the hardness when I find out what it is.

Thanks for everyone's help.

-Kirby

I would guess that there was some misalignment or something moved or grabbed when the attempt was made. I have reamed many hundreds of tapered pin holes and never once did a reamer break. Check what the guy was doing and how he had the work held. If it's a small item I would not recommend using a powered drill to ream it unless you hold the part in a vise. A bench vise is fine. Just needs to be held so it can't jump when the reamer bites in along the whole length. Using a tap wrench to drive a small tapered reamer is fine too, it doesn't take long for small diameter holes.

There's no way to answer the "will hss finish the job" question without knowing the hardness of the part. If it's 45Rc or below yes. If it's harder than that it will likely be difficult to impossible. In hard material, make sure that he is using plenty of cutting oil regardless of reamer type. And ditch the pilot next time. Unnecessary. It may have been what caused your breakage problem.

Can I ask why you changed from a parallel pin to a taper pin ?

I've taper reamed hundreds of holes over the years without breaking a reamer. Normally I used a tap wrench but I have used a cordless drill if the circumstances allowed it. You have to take it easy though, you'll be cutting on all the effective length of the reamer, it's not like drilling with an ordinary drill bit. Taper reaming into any sort of hardened steel I'd use a tap wrench and some cutting fluid. A 1/8" + reamer in a cordless drill is a being a bit ambitious.

Regards Tyrone.

The change was per customer requirements. I tested the hardness and it was reading between 35 and 45 HRC, so hard, but HSS might work to get a part out the door. Any suggestions for a quality taper reamer from MSC? They have 15 from $20 to $45, but price don't always mean quality.

Thanks Tyrone and eKretz.

-Kirby

IME you won't go far wrong with anything Dormer, but use it by hand & carefully at that '' feel your way'' and with plenty of high quality cutting oil and frequently clearing chips.

Again IME small taper pin reamers and power drills only ever end in tears.

Just my take, YMMV

Kirby-Wan said:

The change was per customer requirements. I tested the hardness and it was reading between 35 and 45 HRC, so hard, but HSS might work to get a part out the door. Any suggestions for a quality taper reamer from MSC? They have 15 from $20 to $45, but price don't always mean quality.

Thanks Tyrone and eKretz.

-Kirby

Click to expand...

I'd be having a word with the customer with a view to using a "See-Lok " pin or a spiral roll pin instead. Much easier to install and remove, plus they won't fall out.

Good luck with it anyway.

Regards Tyrone.

Limy Sami said:

IME you won't go far wrong with anything Dormer, but use it by hand & carefully at that '' feel your way'' and with plenty of high quality cutting oil and frequently clearing chips.

Again IME small taper pin reamers and power drills only ever end in tears.

Just my take, YMMV

Click to expand...

For the vast majority of guys out there you are probably right. It always amazed me how many machinists and millwrights there were that I've worked with over the years that had no "finesse" and always tried to brute force everything. Of course when it was the welders I was never surprised...

Kirby-Wan said:

The change was per customer requirements. I tested the hardness and it was reading between 35 and 45 HRC, so hard, but HSS might work to get a part out the door. Any suggestions for a quality taper reamer from MSC? They have 15 from $20 to $45, but price don't always mean quality.

Thanks Tyrone and eKretz.

-Kirby

Click to expand...

Go with a decent brand name and you should be fine.

Yeah, this is a Service Bulletin on an aircraft butterfly valve that changes the straight pin to a taper pin with a cross hole for lock wire. The part connects the shaft to the lever that activates indicator switches which have to trigger within ±1°. If the straight pin had any slop it would slowly deform the switch lever and make it go out of tolerance. So in short, neither I nor the customer has any latitude without going back to the manufacturer outside of choosing to apply it or replace everything.

Thanks for everyone's responses, I'm going to give this a try myself on a scrapped shaft with one of the HSS taper reamers I ordered.

-Kirby

Kirby-Wan said:

Yeah, this is a Service Bulletin on an aircraft butterfly valve that changes the straight pin to a taper pin with a cross hole for lock wire. The part connects the shaft to the lever that activates indicator switches which have to trigger within ±1°. If the straight pin had any slop it would slowly deform the switch lever and make it go out of tolerance. So in short, neither I nor the customer has any latitude without going back to the manufacturer outside of choosing to apply it or replace everything.

Thanks for everyone's responses, I'm going to give this a try myself on a scrapped shaft with one of the HSS taper reamers I ordered.

-Kirby

Click to expand...

Obviously if it's a requirement on an aircraft component that puts an entirely different complexion on the job.

Good luck with it, Tyrone.

Wow, Having just joined this board I'm surprised at how much traffic it gets. Anyway, update on this job:

We got the HSS tapered reamers in and used a T-handle by hand and it took about 5 minutes to ream the 35-45 HRC shaft. I was so excited to get the reamers in I forgot to go get some oil when I tested it on a scrapped part and had no problems. Brought it over to the machine shop and had them do the production part and he was able to do it with no issues either, and he was smart enough to use oil. As an engineer I can't sign off work done on parts so it has to be done by the guys with actual experience cutting metal.

So, HSS to taper ream on 35-45 HRC is not a problem. Just takes time and hand work so you don't go too fast.

Thanks for everyone's help.

-Kirby

That's good Kirby

FWIW - an old school tip / rule of thumb ;- if an ordinary smoothish hand file will mark it, then HSS will cut it, only the harder the part the slower you go, and to give you a guide based on my own experience, .....when you're towards the limit 10ft/minute** cutting speed for HSS can be ????? getting too fast.

** @ 10ft / minute, a 1/4 HSS twist drill will be doing <> 150rpm

Straight flute taper pin reamers have to be cleared of chips a lot. If you have a change get spiral flute - those are made with a left hand spiral and right hand cut so they eject the swarf out the front. Easier to use under power.