Want to make a tapered reamer

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Brian Rupnow

Brian Rupnow

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I want to make a tapered reamer, of a specific taper angle to machine a tapered inlet on model carburetors I make from aluminum. It will be held in the lathe tailstock chuck, while the carburetor body is gripped in the 4 jaw headstock chuck. So--I need a 16 degree included angle taper, which is less than .195" diameter at the small (leading) end, and greater than .315" diameter at the large (trailing) end.--I have some 1/2" diameter water hardening drill rod. I can turn the correct taper on my lathe. I can make the leading end .188" diameter, and the major diameter will be whatever a clean-up pass yields on the 1/2" diameter drill rod. I can cut 4 "flutes" using an end mill. The thing I'm not sure about is how to machine a back clearance behind the cutting edge of the flutes. I know that it can be filed by hand, because I have built a very similar 45 degree tool for cutting model valve seat faces. It's just that my hand filing is far from being consistent or accurate. Is there any kind of machine set-up that will let me put some back clearance on the cutting edge of the flutes that is more accurate and consistent than hand filing?--Keeping in mind that I have a manual lathe, a small vertical mill, and a rotary table.---Brian
 
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1st thing is you've drawn a left hand cutter, maybe on purpose, maybe not. To cut clearance, simply over rotate the part 10 degrees or so from when you've cut the flute, lower the quill or raise the knee (don't know how big your mill is) and take a pass with an end mill along the edge of the tool to leave a very small land of the original turned profile. Blend with an oil stone or file.
 
Using drill rod/me-silver steel to cut aluminium is fairly straightforward. My own experiences have followed Sparey's in the Amateurs Lathe where he 'halved' or almost halved the taper reamer. Ian Bradley basically suggested a D Bit which machines a flat to cut- leaving a thous or two to avoid snatching. Again, I have yards of more or less corroboration from guys that made Irish Bagpipes as well as my and others efforts in Northumbrian Small pipe making.

I've been stopped by a phone call from another Goldstar who was the Merlin and Griffon expert with me and it has reminded me that LBSC made his injectors using the suggested taper reamers as above.
I got my copy of his Maisie book and Curly gives 4 examples.

Hope this helps
 
Woodster--You're right--I hadn't noticed that I had modeled a left hand tool. It was done very quickly to graphically show what I was talking about. Of course the "real" tool will be opposite of what I have shown. I will give some thought to what you have suggested. Goldstar--You are describing a D bit, which has been suggested on another forum as well. I will consider that also.---Brian
 
Woodster--I am somewhat intrigued by your answer, just having a difficult time getting my head around it. I have changed the model to be a right hand tool with only 3 flutes. In order to set the tool up properly in my mill I THINK it would have to be parallel to the top of the mill table with the rotary table swung at an 8 degree angle to the front edge of the milling table and then plunge cut to the centerline while I move the mill table left to right or vice-versa. If I rotate the tool say about 10 degrees, then take a cut with the side of the endmill, it may give what I'm after. I'm just not sure that the angle of rotation will be where I want it to be. I may have to try this and see if it actually works.
 
Brian Rupnow said:
Goldstar--You are describing a D bit, which has been suggested on another forum as well. I will consider that also.---Brian
Click to expand...

Thank you. Sparey- who made lots of engines and carbs described his a 'Toolmaker's reamer'

Sparey describes it thus as he put his effort against a comparable bought out one,
Small taper reamers, one of which is shown as Fig83, may also be made from silver steel rod, which is turned to the required taper and filed to half its diameter. Harden and temper to dark straw colour.

Curly cut his with a jeweler's saw and then filed.

I confess to being a rather lazy soul and put a series of rods in my faithfull Clarkson and heated them to cherry red and tempered them with an old smelly potato.

So there we are

Cheers

Norman

Sparey's bit( whatever the name) will cut left or right handed
 
Color the lands with Dykem so when you machine the relief you can see how close to the edge. Leave a sliver of Blue and finish with a diamond lap after hardening.
In AL you do not need hardening but why not, is so small it is a quick job.
 
Brian

For a one off taper a tapered D bit is the way to go. When I make mine I cut the taper in the lathe. Then I harden and temper. Because I have a surface grinder I then grind to .001" shy of half the major diameter.
I have friends that do not have a grinder that mill to .002" shy of half and then hone the final edge.
They cut fine in Alu, brass and bronze.

Dave
 
Dave--It's not really for a "one of". This particular size of carburetor works very well on all of the engines in the size range I build, so I was thinking in terms of a "permanent tool".--However, yes, if I make a tapered D bit from drill rod and harden it, it would become "permanent tooling".
 
Hi Brian,i have successfully made tapered D bits in the past
They are cheap,easy to make and work well in alum/brass
Success depends how accurate you get down to CL.I use silver steel
harden and temper to blue i recall.Straw for screwdrivers.I also have old std taper
reamers but dont know the angle offhand. Barry
 
I was having a bit of a think and recalled that Derek Brooks writing in Model Engineers Workshop described making a 'baby' Clarkson tool and cutter grinder which was essentially a simplified Stent. Again, he was making small items for model engines such as needle valves. OK, making a Brooks or the John Moran 'Gadgetbuilder' variant is far less effort than- say making a Quorn, it is still time consuming.

If all that is required is grinding a flat on the end of a bit of metal or doing a lathe tool, it takes or is claimed to take a week to make a Tinker which is marketed as plans - in Canada by Guy Lautard. Apart from the ingenuity of Norman Tinker's thinking, it is simply sweeping a tool across a grinding wheel.
Not that there is anything wrong with that. I know from my aged plans that it will do end and slot drills as well. No castings are required- only a cheap Chinese 6" grinder.

Certainly it is worth more than a dismissive read


Norman
 
Brian, I made a d bit tapered reamer and it made a really nice smooth finish in aluminum for my cicada build. used drill rod, cut it and hardened it, then into the oven for about 45 mins at 400 degrees and it cut like butter.

page 5 post 46 here http://www.homemodelenginemachinist.com/showthread.php?t=23533&page=5

but that fluted cutter in your drawings would be interesting to see made as well. beyond my skill level but really neat.

IMG_0090.jpg


IMG_0094.jpg


IMG_0097.jpg
 
I have used tapered endmills for die sinking for injection molds for many years, They work well in a milling machine using a controlled feed such as a locked quill and infeeding with the table Z. But, be very careful if you try to use one in a lathe tailstock as they will try to screw them selves in to the work piece as the backlash ils taken out of the tail stock feed screw. Can really ruin your whole day as they are really aggressive about doing this.

I use a 12.5 degree included angle on my venturi as that is the angle on a standard T handle repairmans taper reamer. They have straight flutes so they can be used in the lathe tailstock. They are cheap (8 to 15 US$) and with the handle removed they can be chucked. The 12.5 degree angle is for the General brand and others may be different,
Gail in NM
 
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Gail--Thanks for the heads up. I will make sure I try this new tapered mill on some junk stock before using it on a semi-finished carburetor body. There seems to be about .018" linear "slop" in my tailstock chuck (I just tested it with a dial indicator and magnetic based stand.). My Solidworks program tells me that this makes a total of .005" difference in the diameter, which shouldn't be a huge concern on a carburetor air horn, as nothing has to mate with it. I will certainly keep this in mind.----Brian
 
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I've seen D-bits used when the throat shape called for a specific curved venturi. The bit is slowly reamed into a pilot hole to a stop depth & yields a consistent, reproducible shape (I would think more a production tool?).

But since you are contemplating a straight taper, why not just get a nice little boring bar for the tool post, set the compound to whatever angle, then you can cut any taper or diameter you desire? I used this same tool to make curved venturi shape but by a series of diameter steps to a cad profile, then smooth over the little mountain tops with a swiss file.

2014-12-09_17-08-48.jpg
 
petertha said:
Coincidentally this website was referenced in another thread & he does some similar cutting tool magic

http://www.deansphotographica.com/machining/projects/mill/cbore/cbore.html
Click to expand...

Hi Peter,

My first attempt was a failure.Have yet to back track and see what went wrong.
Will trying again since I have some Silver Steels bought from HongKong stockist.
I have a good reason as counterbores bought from Newman was not to my liking.The OD was too big. I am about to finish up the DIY Power Feed for my mini mill. Will post if I get the flutes and cutting angle done right.;)
After this will try making the taper reamers.
 
Brian Rupnow said:
Gail--Thanks for the heads up. I will make sure I try this new tapered mill on some junk stock before using it on a semi-finished carburetor body. There seems to be about .018" linear "slop" in my tailstock chuck (I just tested it with a dial indicator and magnetic based stand.). My Solidworks program tells me that this makes a total of .005" difference in the diameter, which shouldn't be a huge concern on a carburetor air horn, as nothing has to mate with it. I will certainly keep this in mind.----Brian
Click to expand...

Agreed about the relatively 'huge' or marked difference because sloppy chucks.

I tried to avoid comment but several things spring to mind. I have a finishing Morse taper reamer which is on a No2 Morse taper:confused: It's fine to clean a ragged existing MT body but will jam without warning and pull the tailstock forward because in this operation, it is not locked down.
Again, unless your drill chuck is both accurate and grips firmly, it will probably pull out the reamer.

I was mulling over the problem and alloy is a so and so. I would be heading for a Morse taper adapter with a grub screw to take the reamer- once a locating flat has been ground in it.

My random thoughts are how cheap these reamers are. Absolute horrendous amount of wear on an abrasive wheel-or perhaps 3, making one. Not me, we once ground a scrap reamer into a No2 MT test bar.

Good luck

Norman
 
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