Reaming tapered through hole in HRC 45 steel

rickbrennan · Feb 12, 2019

I'm having trouble with machining for a tapered pin in HRC 45 round stock. The pin holds the main landing gear leg in the fuselage mount for an experimental aircraft. We step drilled using a progression of lettered drill bits before using a tapered high speed steel straight flute reamer on a Bridgeport mill at 60 rpm. We used flood coolant, cleared chips every 5 seconds or so by backing out and blowing the reamer off with compressed air. At first the reamer cut well. About .100 short of the minimum pin depth, the reamer stopped cutting.

I looked for a carbide tapered reamer, but all I seem to be able to find are HSS. Not sure if we work-hardened the taper, or what the problem is. Recommendations would be appreciated.

E189552 · Feb 12, 2019

What material type & stack up are you reaming?
Are you using cutting fluid or paste?
Hand feeding or trying to power Feed?

Delw · Feb 12, 2019

are all the steps out of it now? if not buy a couple more reamers. I believe the steps are what is screwing up your reamers. on step drills in harder material you should have a rougher a semi rougher and a finisher .
those sharp steps left from the drills wear inserts out extreamly fast go slower and use oil it may help.

atex57 · Feb 13, 2019

If the surface has work hardened then you might have to go in with a die grinder and a burr or stone to get rid of that surface, it should not be very thick.
Ream it at low speed and a lot of feed to keep it from happening again. Put a piece of tape or a mark on the reamer to mark where to stop. Starting and stopping are the places it hardens.

Ed.

TeachMePlease · Feb 13, 2019

How large of a hole are we talking about? I can recommend several different companies that would happily make you a one off carbide tapered reamer, but who I recommend depends on size...

Milland · Feb 13, 2019

TeachMePlease said:
How large of a hole are we talking about? I can recommend several different companies that would happily make you a one off carbide tapered reamer, but who I recommend depends on size...

I wonder about the quality of the HSS reamer he's using, as well as if the stock has hard spots that are dulling the tool. If these are good reamers, and the stock's not crap, then maybe there's not enough force being used to drive the reamer in, and it's being allowed to rub.

If he has to get a carbide reamer, I'd go for one with as heavy a core as possible, and just use it when the HSS gives up. Otherwise I worry about the reamer snapping in the part, there's a lot of engagement. This means having to clear the chips more frequently, and being careful not to jam the reamer in when returning into the hole.

guest · Feb 13, 2019

^^^ Yeah, I'd be a little reluctant to go after it with carbide too, esp on a BP.

The tool pressure is going to go way up as the steps go away and the contact area increases. OP will need to slow the rpm and increase the feed pressure. Heavy cutting oil will work better than coolant.

Would be nice to know the size and material. 4130 V-Mod? 15-5?

rickbrennan · Feb 13, 2019

All the steps are out. Using Tap Magic cutting oil

rickbrennan · Feb 13, 2019

material: 6150
Diameter: 1.600"
Using cutting fluid - Tap Magic cutting oil
Hand feeding on Bridgeport Series I with moderate to heavy pressure, 60 RPM

rickbrennan · Feb 13, 2019

The stock is high quality 6150 - production manufactured landing gear leg. Leg diameter is 1.600". The hole is ~ .375 at large end, B&S #2 taper (.5" per foot). We just ordered another reamer from our aviation tool supplier (usually high quality tools) and are going to try hand reaming without chucking in the mill when we get it . . . unless someone has a better idea.

rickbrennan · Feb 13, 2019

Do you have a recommendation for suppliers of carbide tapered reamers? It's a B&S taper (.5 per foot)and we used a #2, then #3 to get the slightly over .375 large end diameter.

rickbrennan · Feb 13, 2019

B&S #2 taper (.5 per foot). just over .375 at the large end now. We need to go another .100 deeper to get the pin to the specified depth. Using a #3 HSS reamer.

Milland · Feb 13, 2019

rickbrennan said:
Do you have a recommendation for suppliers of carbide tapered reamers? It's a B&S taper (.5 per foot)and we used a #2, then #3 to get the slightly over .375 large end diameter.

What we're thinking is a custom reamer, with a higher flute count but shallower gullet depth to maintain core strength. Not an off the shelf item.

But before we get that far, what's the brand of the reamer you have now - same as the new one you've ordered? Can you take a close-up picture of the cutting edges, so we can judge if they're worn out?

Your Bridgeport probably can't go slower than were it is right now, but doing this by hand or portable drill isn't a great idea. If this is for aircraft use, you want to get the best form accuracy that you can from the final hole.

Speaking of aircraft, is this really the best way to retain the landing gear? Is there any secondary feature (like a ring) that retains the pin if it should loosen in the hole? Can you post a pic of the actual parts, so we can get a better handle on it?

guest · Feb 13, 2019

I was imagining a much larger hole. A B&S #2 is only 1/4" at the small end. Even if you could find one, I would not use a solid carbide reamer on that hole for fear it would grab and shatter.

I'd stick with the HSS- at least it's forgiving. 60 rpm is only 6 sfm on the 3/8" dia- that's pretty slow, but the surface area being cut vs. the strength of the tool is not in your favor.

If it was me, I would worry the damn thing out by hand, or take another swing at it in the spindle with a fresh reamer.

If you go by hand, put a tap wrench on it, and liberal use of your cutting oil. Put a center in the spindle of the BP, and have someone apply down pressure on the quill while you operate the wrench. You have to keep that reamer cutting- rub just a little, and it will dull quickly. You will have a better feel for when it's cutting if you do it by hand. As long as you can feel it cutting, keep going.

You're gonna be there for a while, would have been better to rough it out before heat treat.

There are a few flavors of Tap Magic. The thin stuff for aluminum is not very good for this application. A heavy cutting oil would be better.

I don't think you have work-hardened anything. 6150 is a common spring steel, and is pretty resistant to plastic deformation.

sfriedberg · Feb 13, 2019

A large taper reamer is actually sort of hard to drive, due to the large surface area. Worse than a drill of the same diameter, and way way worse than a cylindrical reamer of the same diameter. You probably need more feed pressure than can be applied by hand with any finesse.

I have to do the occasional MT3 or MT4 socket, both much larger than the size OP is dealing with. When I can't bore them on the lathe, I plan to use step drilling and both a roughing and a finish reamer. Lots of flutes can make the feed pressure issue worse, so if you're going to commission a custom carbide finisher, I'd suggest sizing the flutes for "lots", but have only 1/2 or even 1/3 of the flutes actually ground out, with the areas between flutes slightly relieved below the cutting cone surface. That would also enhance the core strength.

rickbrennan · Feb 13, 2019

The pin is a standard aircaft part. It's threaded at the small end. The landing gear leg fits into a tube in the engine mount assembly, retained by the tapered pin normal to the gear leg and tube. You tap the tapered pin in to get a snug fit, then retain it with a nut. After many landings, if there is some wear at the pin-tube point you tighten the nut a bit to take out any slop. Works great.

sfriedberg · Feb 13, 2019

Yes, that's a classic detail.

rickbrennan · Feb 13, 2019

View attachment 249612 View attachment 249613 View attachment 249614 View attachment 249615

Images of the setup on the mill . . .

rickbrennan · Feb 13, 2019

I think what happened is I used flood coolant first, and pecked at the hole, reaming for about 5 seconds at a time. That chowdered my reamers. Later, I switched to Tap Magic, but the damage was already done and I didn't get much further. I like the idea of chucking the new reamer in a tap wrench and using the mill to apply pressure while turning the reamer by hand with lots of cutting oil. I'm guessing that will give us much better results. I'm used to straight reamers where I run them down through the hole with very little resistance. Completely different than the effect you get with a tapered reamer. Thanks for all the input - this is a great forum.

Milland · Feb 13, 2019

Looks like a good setup, and yeah, you should try the manual/mill approach and see how it works out. Another option might be a cobalt reamer, that might be available OTS. Cobalt alloys are more brittle than regular HSS, but much less than carbide.

Would still like to see a picture of the reamer when you get a minute. Did you try uploading additional pics and they didn't make it?

Reaming tapered through hole in HRC 45 steel

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