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Author Topic: How much jump before pellet hits the grooves?  (Read 3085 times))

Offline rsterne

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Re: How much jump before pellet hits the grooves?
« Reply #60 on: November 13, 2021, 12:30:24 AM »
Here is a photo of one of my custom chamber reamers.... and no, I do not make them for sale....  ;)



The pilot portion is a thou or two smaller than the land diameter and the tapered cutting flutes start smaller than the lands and taper up to the chamber diameter.... Behind that point the diameter is constant.... Here is a drawing of a .22 cal version....



The step down behind the pilot is about 0.010" to where the flutes start.... Here is a generic drawing with the dimensions of the flutes in calibers....



The dotted blue lines are for a single flute, the solid blue lines for a three flute.... The depth that you plunge the mill past the centerline provides an angle to the cutting edge.... The deeper it is, the faster the reamer cuts, while the closer it is to the centerline the finer the cut and the smoother the finish.... I use 5% of the caliber, as shown in the drawing....

I have not used a modified pin reamer, but others have, and very successfully.... I understand that the flutes are simply ground away where the taper reaches the desired chamber diameter, and do not touch the barrel at all behind the tapered part.... As such, that could be done with a hand grinder....

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Re: How much jump before pellet hits the grooves?
« Reply #61 on: November 13, 2021, 01:53:10 AM »
Thank you, Bob
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Offline lennyk

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Re: How much jump before pellet hits the grooves?
« Reply #62 on: November 13, 2021, 01:05:48 PM »
Will a straight flute be much harder to use than a spiral flute due to the "biting/chatter" ?
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #63 on: November 13, 2021, 01:34:20 PM »
Will a straight flute be much harder to use than a spiral flute due to the "biting/chatter" ?

That's a good question and one that I can't answer yet. And since the company that shipped the wrong reamer still hasn't got the correct one to me, I'm glad I bought a second. I have a spiral flute in hand and will start making my grinding rig next week. That will give me time to cast the chamber and double check sizes.
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Offline nervoustrigger

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Re: How much jump before pellet hits the grooves?
« Reply #64 on: November 13, 2021, 01:55:34 PM »
Will a straight flute be much harder to use than a spiral flute due to the "biting/chatter" ?

If you intend to do the operation by hand, a left-hand spiral reamer will help immensely because it resists self-feeding.

The number of flutes will also have a big influence on how it behaves.  For example, the worst case would be a reamer with exactly the same number of flutes as there are lands in the barrel.  That sets up a repeated grab then release.

If instead you can use a suitably rigid setup in a lathe, it's not nearly so much of a problem.  Feed really slowly and don't let the flutes clog up.
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Offline rsterne

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Re: How much jump before pellet hits the grooves?
« Reply #65 on: November 13, 2021, 02:31:26 PM »
I run my lathe at about 50 RPM and feed VERY slowly, removing the reamer every 0.1" of feed depth to blow off the chips and relube it with cutting (tapping) oil.... The chips are so fine they are basically dust....



Photo above showing reamer withdrawn for cleaning/lubing.... Note that all the cutting occurs in the tapered middle of the flute length, the front is smaller than the lands, and the back is the parallel chamber section.... You can click on the photo to enlarge it.... Here is a photo of a reamer after use.... You can see the polished area in the middle where the cutting occurs....



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Re: How much jump before pellet hits the grooves?
« Reply #66 on: November 13, 2021, 06:55:56 PM »
Having a different number of reamer flutes to the number of lands in the barrel helps break the resonance, when reaming using a piloted reamer.  However, if the reamer is unpiloted, then the cutting force can spring the front end of the reamer and set up a vibration that may be worse than with a matched flute and land count (even if the latter has no pilot).  This deflection is worse with small calibers because the reamers are much more flexible.

Some reamer manufacturers space their cutting flutes slightly unevenly to break chatter producing resonance.   Whereas the lands in a 6 groove barrel should all be spaced evenly.

A lefthand spiral flute, right hand cut reamer is preferred if you can get one in your size, because they do not "screw in" when cutting (as noted above), and produce the smoothest, most controllable cutting action.  Righthand spiral flute reamers cut aggressively at low axial force, thus do not produce as smooth a finish as a lefthand spiral flute reamers.  A straight flute reamer is most prone to chatter, or cutting lobed holes, but can work fine when the user knows how to prevent chatter.  This starts by turning the reamer very slowly and feeding it gently and smoothly.


Getting back to Greg's reamer grinding; to create a pilot on a standard taper pin reamer will require adding metal to the reamer nose, not just grinding it away:  If you look at Bob's reamers, the pilot matches land diameter (minus 0.001"), then the tapering section behind the pilot is actually smaller than land diameter.  Some distance away, the taper in the reamer gently meets land diameter, and cutting starts.

How to convert a taper pin reamer to a piloted reamer then?  Easy:   Grind a sub-land diameter cylindrical section on the reamer nose, to look like an undersize pilot.  Then add what looks like a short section of brass tube on that HHS mini-pilot tp form the actual pilot. 

The brass pilot OD is sized 0.001" below land diameter to guide the reamer.  It is not essential that the pilot be free to rotate on the reamer nose, because then you need to be devise a means to prevent the brass pilot from falling off the end of the reamer, each time you remove the reamer from the barrel to clear chips.  The brass pilot can be a light friction fit to the sub-pilot on the reamer nose.

Rather than use 10,000 words to describe such a piloted reamer conversion, I figured pictures might help - attached below.   For reference, the sub-pilot diameter and length given are arbitrary, but will work in practice.   Likewise, the relief angle grind beyond the max .358" diameter section of the reamer is 1 degree per side, with an arbitrary but reasonable clearance length.


Images below start by comparing the modified taper pin reamer next to the stock one:
« Last Edit: November 13, 2021, 07:23:41 PM by subscriber »
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #67 on: November 13, 2021, 08:42:47 PM »
That's exactly what I'm going to do to make a pilot. I could only get stock sizes of tubing, so around .340 diameter which still leaves a bit of room to move around. To minimize this I'll extend the length of tube and might even try to flare the end a bit. A bit of epoxy should hold the tube in place.
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #68 on: November 13, 2021, 08:45:12 PM »
By the way, those drawings are great!
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Re: How much jump before pellet hits the grooves?
« Reply #69 on: November 13, 2021, 08:57:49 PM »
You could use you mill as a lathe, after attaching the section of brass tubing to the ground down reamer nose.  This 3/8" diameter brass tube could work for that:  https://www.mcmaster.com/7782T431/

I would not have a long section of tube hang off a short "boss" on the reamer nose.  The chances of angular error between the tube and reamer are significant.  Also, on drawn tubing intended for fluid flow, the ID and OD may not be concentric to 0.001".  The diameters, unless measured are nominal for any given tubing; and may be larger or smaller - also out of round....

You really need the reamer pilot OD to be close to land diameter for it to offer any useful support. 

One aspect that you need to evaluate is if simply gripping the reamer stem in your mill collet has the reamer run true; in terms of run-out and angularity (within reason).   If the reamer does not run true, first regrip it in the collet with a 90 (and then 180 and 270) degree rotation relative to the collet, to see if errors are stacking, or can cancel out.  Place the reamer stem as deep as it can go into the collet, without actually stopping on the collet holder.

Else, you may need to use the center dimple on the end of your reamer to force the front end of the reamer to run true, while spinning the reamer vertically in the mill.  If you have to support a wobbling reamer via a center attached to the table, then you will need to use a hand file to "turn" the pilot OD down. 

If the reamer runs true without supporting the small end, then use the mill vice to hold a sharp lathe tool, to turn the brass pilot to a known size, reasonably coaxial to the section of reamer flutes that will do the chamber cutting. 

You can use a single flute of a stationery endmill ideally positioned, and clamped in a vice (by its shank) as a lathe tool.  This assumes you have no lathe tools such as a boring bar - something that can also be used in a mill to bore holes.  If you have a broken endmill you can grind that into a lathe tool to cut brass.

You could also use your Dremel with the diamond wheel / cutter to abrade the brass pilot just like you plan to for the reamer.  This should be OK for a small amount of brass removal, as long as diamond grit does not shed off the wheel and imbed in the brass pilot OD.
« Last Edit: November 13, 2021, 09:18:07 PM by subscriber »
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Re: How much jump before pellet hits the grooves?
« Reply #70 on: November 13, 2021, 09:01:22 PM »
By the way, those drawings are great!

Thanks.  It helps to start with a free 3D model of a reamer :)

I can think in 3D, but without real scale, can easily imagine the equivalent of an Escher sketch, where anything seems possible.  Seeing a scale correct representation helps me think more clearly, and I enjoy creating that to help others.
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #71 on: November 13, 2021, 11:42:46 PM »
All of the brass tube I found was 0.014 wall thickness so the next larger size is too thin. But I'll look again because I had to buy a pack of many sizes, price was the same as one piece of the .0340 tube.

Maybe I can solder a larger tube to the 0.340 tube and cut it down as you mention. I have a few dull or broken tools that I saved that I can grind into other things.

Could I silver solder the 0.340 tube to increase diameter and then cut it down? Or is silver solder approaching the "too hard" range? Talking pipe silver brite type solder, but I also have electronics silver solder too.

My thinking with a long but undersize pilot is that the drift is an angular issue. A long pilot would reduce the drift angle at the cutting location by acting at the far end. It does assume a straight tube, which might be a big assumption. Also assumes the tube will not bend. But even something 0.010 undersize is better than the 0.030 undersize of the cutter, and also prevents unwanted damage from the end of that cutter swinging over into the barrel.

Maybe I should rethink drilling a hole in some Delrin and cutting it down to proper size for a pilot. The tubing seemed like a quicker way to get finished. Or a piece of hardwood, I have some 3/8 oak dowel that would be easy to work with and for one or two uses it would probably be fine. Just need to grind down about the first quarter inch from the end of the reamer to make a spot to fit.
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #72 on: November 14, 2021, 12:21:11 AM »
I just measured the brass tube again, it is a telescopic set of tubes and fits most of the way down the next size up with zero binding, so they must be straight. Size is 0.345 inches or somewhere in the 0.005 to 0.007 undersize. The error that I might get from this amount of difference probably isn't enough to worry about. Need to hit 0.315 on the small end grind to install it and epoxy in place, the reamer starts at 0.322 so not a lot to remove making the job easier. If I get to 0.317 I can probably heat the tube to shrink it in place, and make up another 0.002 in the process.

If I can get a good fit on the chamber end, I think errors will be small enough to be fine.
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Re: How much jump before pellet hits the grooves?
« Reply #73 on: November 14, 2021, 12:31:53 AM »
Bright silver solder is 90+ % tin.  So, not too hard.  Not sure you can "build up" a brass tube with it by more than perhaps 0.004" in diameter.  Maybe not that much.

I think you want the reamer to find its own center on the conical cutting flutes, with the pilot used to help the other end center in the bore, and prevent any rocking moments.   The drive end should be allowed to float, by turning it with a symmetrical handle by hand; concentrating on not applying unbalanced side loads.

You may be able to make a long pilot, but my instinct says that it is not going to allow the reamer flutes to act as the other center of rotation.

If you have Delrin and can use the mill as a lathe, that might be even better pilot material than brass - as long as you don't drop the reamer on a concrete floor and imbed grit in the Delrin.

My suggestion is to study chamber reamers with pilots.  Pilot lengths seems to fall into a narrow range.  It seems to me that they vary in length from 1/4" to 3/8"; regardless of caliber.  Bob may have more insight into this, but I almost feel like a barrel shaped pilot would be perfect.  It would stabilize the front end of the reamer concentric with the bore, then allow the rear end of the reamer to self align in the cone it cuts, based on the average position of the lands and grooves.  That way, all of the rotational torque you feel will be from cutting, rather than from friction due to the pilot applying angular moments to the reamer.  A counter argument is that free spinning pilots exist for this exact reason.
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Re: How much jump before pellet hits the grooves?
« Reply #74 on: November 14, 2021, 12:44:17 AM »
I suspect there are many ways to make this work.  You could solder the tubes together if you need to increase the diameter. 

Heat shrinking the tube on should work.  If the tiny thermal mass of the tube is enough to get it on before it cools.   If it cools before it is home, I think you can tap it the rest of the way: 

You could also leave the reamer "boss" 0.002" larger than the brass tube ID; then tap the tube with a very light mallet (or screw driver handle) to seat it on the reamer nose.  The friction will hold it in place and swell the tube OD by about 0.002".  If driving the tube on, break the sharp front corners on the pilot "boss".  I showed them sharp in the 3D model, but if you are using imbedded diamond cutters, you could break those edges to make getting the brass tube on easier. 

The fact that a lot of the original reamer flutes are still present need not matter - unless the tube stretched over it is lobed by more than 0.001" - or enough to ride up and down on the lands in an obvious manner.  You might argue that a looser fit held with epoxy avoids making the brass tube lobed.  I would concede that.
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Re: How much jump before pellet hits the grooves?
« Reply #75 on: November 14, 2021, 07:39:49 PM »
I don't have a lathe, but I might be able to rig something on my mill. Put the reamer in a collet and a rotary tool on the table. I'll have to look at that as an option since it would be far more accurate than a bench grinder. Height is my biggest issue here, only have a little desktop micro mill, but I've never let it stop me from doing projects bigger than it can handle.

LMBO  You work in enough job shops and doing too big jobs on too little equipment becomes second nature. You know how it goes,"we expect you to walk on water and do the impossible and we want it done yesterday!"
Here is a photo of one of my custom chamber reamers.... and no, I do not make them for sale....  ;)



The pilot portion is a thou or two smaller than the land diameter and the tapered cutting flutes start smaller than the lands and taper up to the chamber diameter.... Behind that point the diameter is constant.... Here is a drawing of a .22 cal version....



The step down behind the pilot is about 0.010" to where the flutes start.... Here is a generic drawing with the dimensions of the flutes in calibers....



The dotted blue lines are for a single flute, the solid blue lines for a three flute.... The depth that you plunge the mill past the centerline provides an angle to the cutting edge.... The deeper it is, the faster the reamer cuts, while the closer it is to the centerline the finer the cut and the smoother the finish.... I use 5% of the caliber, as shown in the drawing....

I have not used a modified pin reamer, but others have, and very successfully.... I understand that the flutes are simply ground away where the taper reaches the desired chamber diameter, and do not touch the barrel at all behind the tapered part.... As such, that could be done with a hand grinder....

Bob
  Very smart, in effect you've created a single flute, front piloted gun drill, That and having the leading angle going below bore size to eliminating shoulder trouble and insuring a clean edge. Did you rotate the tool under power or slowly by hand? Sometimes hand rotation prevents a cutting edge from biting or chatter .
« Last Edit: November 14, 2021, 07:42:52 PM by Spin »
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Re: How much jump before pellet hits the grooves?
« Reply #76 on: November 14, 2021, 07:53:23 PM »
Did you rotate the tool under power or slowly by hand? Sometimes hand rotation prevents a cutting edge from biting or chatter .

I believe Bob already clarified that, quoted below for convenience:

I run my lathe at about 50 RPM and feed VERY slowly....
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #77 on: November 15, 2021, 04:46:12 PM »
Couldn't get it to fit in a collet, I only have little MT2 collets in end mill sizes. The shank is 0.410 which doesn't fit anything I have. So I fell back on putting it in my rotary table and 3 jaw chuck. After much messing around, my DTI reads total run out of around 0.0005 to 0.0007 on the big end, and closer to 0.001 on the small end. Small end is difficult since I'm measuring on the cutting edges and jumping off and back on the flutes could introduce errors.

I'll have to put the diamond grinding wheels in an 1/8 collet and hope for the best.

This reamer is the longest object I can do this way, the little table is out of room for clamps!
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Re: How much jump before pellet hits the grooves?
« Reply #78 on: November 15, 2021, 06:31:40 PM »
Greg,

That looks OK.  0.001" total runout at the small end means the reamer will cut more on some flutes than others.  While less than ideal, remember that a single flute reamer works.  You just have to proceed more slowly. 

The eccentricity also means that the tapering reamed hole might end up 0.001" larger in diameter than the reamer measures at the corresponding distance from the pilot.  This wider cutting effect would be biased towards the pilot, and diminish towards the wide end of the reamer.   The overall effect is to cut a slightly shallower angle than the taper pin reamer has from the factory.   No big deal.   

Why my assumptions stated above?  The pilot to max cutting OD distance is a little over an inch - image below.  This is based on my assumed pilot dimensions; rather than yours.   

My advice is to break the front and rear corners of the pilot OD at a shallow angle or radius, so that the pilot does not tend to bind against the lands, due to the slight angularity the unavoidable eccentricity might induce.  The image below shows a tangent radius at the pilot OD, to help the pilot slip into the bore and follow the cutting action, without hindering either axial or rotary motion.

I think your setup will work fine.  The important question is what is this barrel's groove diameter at the breech?  Determining that with the Cerrosafe, before you grind the relief at max functional reamer OD is required.  Knowing the land diameter will let you make an appropriate pilot OD.

From the bad barrel; you already have some idea if a .358" cylindrical cut will clean up the lands and leave a chamber that the projectile diameter you intend to shoot loads into easily, yet without obvious slop.  Part of this question is if you plan to size projectiles to exactly groove diameter; a little over, or a little under.   

If the parallel chamber ends up 0.002" larger than the projectile, instead of 0.001", is there any real loss?  Somehow I think that the long taper into the lands after the chamber will center the projectile either way.  Also, a diametral clearance of 0.002" on .357 chamber is less significant, than on a .177.  Partly because of the absolute diameter; and partly due to the longer projectile bearing length in .357.

You no doubt will polish the chamber and tapering lead after reaming.  That will open up the parallel chamber by perhaps 0.001" to clean up the finish.  How to polish the chamber is easy, but also easy to mess up.  So will require some thought and some planning - if you have not done it before.

« Last Edit: November 15, 2021, 06:35:05 PM by subscriber »
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #79 on: November 15, 2021, 07:54:02 PM »
Once again, your diagram provides great info and cements what I thought I was seeing.

The Cerro safe arrived today so I'll have to get messing with it tonight. If it goes well in the junk barrel, I'll pull the good one and measure it too.

The straight reamer arrived today too, I'm thinking I may want to try grinding it first because I think it may chatter, 6 flutes against 6 barrel grooves. The reamer above is 7 flutes so it should chatter less and I'll want to do my best job on it. Also harder to measure because I don't have opposed parts to measure across like I do on the straight flutes.
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