[QuinnSjoblom]

im working on a design that will need a very precise tapered hole in hardened steel, 58-60hrc. Doing it pre heat treat is definitely an option, but i would prefer to do it after if possible for best accuracy and finish. The hole is quite small, 1/4" at the top, 10:1 taper (2.86 deg per side or 5.72 included), and only 1/8" deep, through hole. The reaming operation will be removing very little material, about 6 thousandths off the wall at top edge. This will be done on cnc.

So first question, can i do this in hardened steel with a carbide reamer? From what i understand about tapered reaming, it can be challenging because the whole length of every flute is cutting and it has to take a very small chip. I would imagine especially in hard steel, it will resist cutting and try to rub. should i even attempt this in 60hrc material?

Next question, where do i get such a tool? Ive been searching around without much luck. Morse taper and taper pin reamers are very common, but im not finding other angles, especially not in carbide and not this small. This doesnt need to be exactly 10:1 taper, but something at least close to that for the geometry to work. I will be turning the tapered pin that drops into this hole so the exact angle is not important. I would say between 5 and 6.5 degree included angle should work. Ive searched ebay and found various used taper carbide reamers, but nothing that will work for me. Also i will need to be able to replace this tool when needed, so even if i happen to find the right one used on ebay, thats not gonna help me much. Am i looking in the wrong place, or Is this going to be a custom made tool?

Im also open to other suggestions for making this hole. It needs to have a diameter tolerance of about 5 tenths, locational tolerance of about a thousandth and have a very good finish. I know that "very good finish" is vague, but i dont know well enough to give it an ra. I would say definitely better than what i would get by doing a helical bore with a ball endmill. The mating tapered pin will drop into this hole with about 20oz of pressure and it needs to easily release with absolutely no sticking. To me it seems reaming will be the easiest way to hit these requirements. If its not gonna work, i do have the option of turning this hole on the lathe, but it will be a big awkward fixture and an extra op requiring a lot of setup. I would very much prefer not to do it that way.

Im also not stuck on the idea of doing it hard, theres a good chance it can be done pre heat treat and keep the necessary tolerance. I can measure the change in heat treat and adjust for that. It would just be better to do afterwards if possible.

[deadlykitten]

This doesnt need to be exactly 10:1 taper, but something at least close to that ... I would say between 5 and 6.5

hy turning ? a reamer is not critical, expensive, will require alignment, and may not cut into those 60hrc

do have the option of turning this hole on the lathe, but it will be a big awkward fixture

why is the fixture so tricky ?

It needs to have a diameter tolerance of about 5 tenths

relevant tolerance for conical surface is on z axis, in assamble; just saying

theres a good chance it can be done pre heat treat and keep the necessary tolerance

The mating tapered pin will drop into this hole with about 20oz of pressure and it needs to easily release with absolutely no sticking

to release without sticking, means that the ring must be hard ( so to not deformate ), oiled ( for less friction ), and contact surface to be big ( so les pressure / area )

consistency for those is better if machining after heat treat, but may work even if you make 10eq, heat treat, then chose 3 for example / kindly

[QuinnSjoblom]

I guess i shouldnt have said "turned". I meant the tapered hole could be bored on lathe if it absolutely had to be. Yes, the male taper part will be turned on lathe no matter what and i understand how to do that no problem. The hole is the part in question. It could be held in a fixture for boring on lathe, but trust me when i say it would be very inconvenient to fixture this otherwise mill part on the lathe for one operation. It would require constant changing back and forth of tooling on my lathe and unnecessary setup. its a possibility as a last resort, but i will try all other possibilities first including reaming pre heat treat. This is not a one off part, I am working on an efficient method for continued production.

I guess i didnt specify this is a mill part. reaming would be done on mill, boring would require moving to another machine

[deadlykitten]

okey so is not a revolution part; of course, a reamer now seems more likely

another aproach, is to use a high rev air spindle ( cheap one ) and grind it; unfortunately, i don't know a stone that can cut consistent at such small diameters, because i don't grind much

however, if you have in house a bunch of small stones, you can experiment; it may be possible to consume 2-3 of them per part, but may still be less expensive than whatever else tooling

[mactec54]

im working on a design that will need a very precise tapered hole in hardened steel, 58-60hrc. Doing it pre heat treat is definitely an option, but i would prefer to do it after if possible for best accuracy and finish. The hole is quite small, 1/4" at the top, 10:1 taper (2.86 deg per side or 5.72 included), and only 1/8" deep, through hole. The reaming operation will be removing very little material, about 6 thousandths off the wall at top edge. This will be done on cnc.

So first question, can i do this in hardened steel with a carbide reamer? From what i understand about tapered reaming, it can be challenging because the whole length of every flute is cutting and it has to take a very small chip. I would imagine especially in hard steel, it will resist cutting and try to rub. should i even attempt this in 60hrc material?

Next question, where do i get such a tool? Ive been searching around without much luck. Morse taper and taper pin reamers are very common, but im not finding other angles, especially not in carbide and not this small. This doesnt need to be exactly 10:1 taper, but something at least close to that for the geometry to work. I will be turning the tapered pin that drops into this hole so the exact angle is not important. I would say between 5 and 6.5 degree included angle should work. Ive searched ebay and found various used taper carbide reamers, but nothing that will work for me. Also i will need to be able to replace this tool when needed, so even if i happen to find the right one used on ebay, thats not gonna help me much. Am i looking in the wrong place, or Is this going to be a custom made tool?

Im also open to other suggestions for making this hole. It needs to have a diameter tolerance of about 5 tenths, locational tolerance of about a thousandth and have a very good finish. I know that "very good finish" is vague, but i dont know well enough to give it an ra. I would say definitely better than what i would get by doing a helical bore with a ball endmill. The mating tapered pin will drop into this hole with about 20oz of pressure and it needs to easily release with absolutely no sticking. To me it seems reaming will be the easiest way to hit these requirements. If its not gonna work, i do have the option of turning this hole on the lathe, but it will be a big awkward fixture and an extra op requiring a lot of setup. I would very much prefer not to do it that way.

Im also not stuck on the idea of doing it hard, theres a good chance it can be done pre heat treat and keep the necessary tolerance. I can measure the change in heat treat and adjust for that. It would just be better to do afterwards if possible.

Is this for a Tapered Pin or a Sprue Bush, either you would cut the taper first before heat treating, and lap it with diamond paste to the finished size, sometimes you can find tapered Drills you can use to rough the taper and then use the hand tapered Reamer to finish close to size, heat treat and then lap

Where to get these Reamers, any Mold making supplies will have what you need if it is a standard Taper, DME is a starting point even Ebay or MSC depending on what you need it for Pin Reamers or Sprue Reamers

If the Pin gets stuck, you can add an internal thread, or an external thread if you have the room for it, then you can use a removal tool

[QuinnSjoblom]

I didnt really consider lapping since its a taper, but maybe that would be a good option for machining pre heat treat. Keep in mind this is a relatively shallow taper at 10:1. Ive searched all over google including ebay and msc, not finding anything near the angle i need. Everything standard is much steeper. taper pins are about 50:1, i need 10:1.

This is part of a locking assembly for a folding knife so there needs to be absolutely no sticking. The lock spring tension is about 20oz so theres not much force on it and it needs to release with no more than the 20oz pushing it in. The shallow angle is needed to avoid the sticking. Ive already done a few prototypes of my lock system and it works great. The current design uses flat tapered surfaces but its difficult to get the finish and tolerances needed consistently to avoid lock stick. switching to tapered cylindrical mating surfaces makes it much easier to consistently hit the tolerance and finish needed with minimal hand work, but i didnt foresee it being this difficult to find the tapered reamer needed.

If i wanted to have a custom reamer made at the angle i need, who would i contact for that?

[mactec54]

I didnt really consider lapping since its a taper, but maybe that would be a good option for machining pre heat treat. Keep in mind this is a relatively shallow taper at 10:1. Ive searched all over google including ebay and msc, not finding anything near the angle i need. Everything standard is much steeper. taper pins are about 50:1, i need 10:1.

This is part of a locking assembly for a folding knife so there needs to be absolutely no sticking. The lock spring tension is about 20oz so theres not much force on it and it needs to release with no more than the 20oz pushing it in. The shallow angle is needed to avoid the sticking. Ive already done a few prototypes of my lock system and it works great. The current design uses flat tapered surfaces but its difficult to get the finish and tolerances needed consistently to avoid lock stick. switching to tapered cylindrical mating surfaces makes it much easier to consistently hit the tolerance and finish needed with minimal hand work, but i didnt foresee it being this difficult to find the tapered reamer needed.

If i wanted to have a custom reamer made at the angle i need, who would i contact for that?

You would make it yourself.

If you want no sticking then that in itself will be a challenge, that is the idea of a tapered pin, is to lock parts into place, the less taper you have the harder it will be to remove the pin

They are normally only made from HSS

[QuinnSjoblom]

yes, an angle similar to a traditional tapered pin would be about impossible to not get stuck, but at 10:1 its about 5 times more taper than that. Again, it will also only be pushed in with hardly over a pound of pressure. I suppose it shouldnt be too hard to make one out of hss. Do you have any recommendations for best choice of tool steel, number of flutes, rake angle, and relief angle? I really have no idea what geometry the flutes should have. I do have a 4th axis setup so i suppose i should be able to do helical flutes if thats much advantage, obviously left hand down cutting flutes.

[deadlykitten]

is hard to bit 60hrc with a hss reamer there will be no hrc difference, so may be better to ream before treat

if you still think of reaming after heattreat, then also the reamer needs to be grinded after heattreat, so if you can make a reamer, then is possible to also skip the reamer and grind the part after heat treat ( you may grind them using a special fixture, or inside your mill with an air spindle ) .... is kind of a loop

if you consider reaming before heat treat, then why bother to craft a reamer ? material is soft, simply interpolate a conical helix ... or there is no cnc ?

i can design at least active length, for reference

I really have no idea what geometry the flutes should have.

the part is too short, thus L/D ratio is small, so you are more after a rigid taper endmill; such short 'reamers' have an advantage in chucking fixture, thus they rely less on the flutes to be guided inside the hole; once the tool gets longer and chucking gets less rigid, then the reamer needs the flutes to be guided, and in such a case, helix and more flutes will guide better than few straight flutes, but this does not mean that last variant won't work

obviously left hand down cutting flutes

why ? kindly

[mactec54]

yes, an angle similar to a traditional tapered pin would be about impossible to not get stuck, but at 10:1 its about 5 times more taper than that. Again, it will also only be pushed in with hardly over a pound of pressure. I suppose it shouldnt be too hard to make one out of hss. Do you have any recommendations for best choice of tool steel, number of flutes, rake angle, and relief angle? I really have no idea what geometry the flutes should have. I do have a 4th axis setup so i suppose i should be able to do helical flutes if thats much advantage, obviously left hand down cutting flutes.

If the taper needed is short you could, Grind a D-Bit out of carbide to cut the Taper you need