- Joined
- Nov 16, 2012
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- 5,596
Been meaning to re-make a Brown & Sharpe taper reamer, this time out of O1 tool steel that will be heat treated to RC 60+. This is will be used to make balancing grinder hubs for the B&S surface grinder in my shop. The angle is 7.125[SUP]o[/SUP] from centerline (14.25[SUP]o[/SUP] inclusive) which I believe is also known as 3 in 12 taper. Reamers with this angle are available but I can't find one with the right base diameters.
This metal is a little expensive so I'll want to use as short a piece as possible. To do that, I'll pass along a method of spinning between a 3J chuck and a dead center -and still managing to get perfect concentricity. I'll show step by step and it's useful for folks who prefer not to spin between centers. Normally, I would spin between centers but I'm trying to conserve this piece of stock.
It starts out with this, a hunk of O1 and a CAD drawing with the dimensions of the cutter. The cutting edge diameter goes from 1/2" to 1.1" over a distance of 2.4". I've chosen a 2" long shank to drive it and I'm giving myself a generous extra 1.5" of material for work holding in the chuck and dead center. You should be able to see this in the photo below.
First, lets see how much room there is and if it's even possible in this little space. Here, I'm taking a piece of old brass boat propeller shaft and seeing if there's enough room to work. After thinking things over, I'm going to splurge and cut my piece 7" long instead of 6".
My 3J chuck (just the stock chuck that came with the PM/QMT lathe) is fairly well behaved after some minor tuning and balancing. If your 3J does not re-center well at the same diameter, you should probably switch over to a 4J and scrap your 3J. When a 3J does not re-center at the same diameter, it's got serious problems -probably with the scroll and/or jaw journals.
The trick to this is to always make a mark on the piece and put it in the chuck in the same orientation. Start by facing and drilling one end and making a mark (red spot) that lines-up, in this case, with the insignia on the lathe.
When you've done one side, flip it around and face/drill the other end making sure the mark is lined up with your landmark. Once that is done and without removing the piece after the second face/drill operation, I'm going to reduce the shaft to 1/2". This will later be used to grip the part with the 3J chuck. Note: At this time, we know 2 things for sure. 1) the center hole is concentric with the 1/2" stub 2) the 1/2" stub is concentric with the average outside diameter of the uncut shaft. -We also know that the center hole "should be" pretty well centered with the center hole on the other end. Here's the 1/2" stub:
Now, flip the piece around and grab it in the jaws by the stub. Bring-in your dead center and tighten things down. Make a light pass of about 0.005 DoC. Then measure the shaft left, center and right. On my first pass, I had difference of 0.0046", wide at the tailstock end. This means that the tailstock must be moved toward me by 0.0023".
The next sequence of steps, to move the TS 0.0023", are important to do in the proper order.
First, put a TDI on the end of the part and set it to a zero point (utilizing 1/2 the travel of the TDI). Second, slightly loosen the chuck jaws so they are still grabbing the piece but not loosely. Third, move the TS head by 0.0023". On my new TS, lateral adjustment can be made without unlocking the base from the ways. My finger is pointing to the lateral adjustment on this TS. If you have a traditional TS, making this adjustment may take a little trial and error. Once the adjustment is made, tighten everything backup. In my case, after tightening the chuck, I loosened the TS base slightly and re-applied sufficient dead center pressure. This TS does not lose center when the base is loosened and re-tightened.
And finally, take another pass and re-measure the shaft diameter at left, center and right.
In this particular case, the shaft came out measuring 1.3197" 1.3198 and 1.3199; thus, it is holding +/- 0.0001" -Good enough for this piece because it will be cut to rough form and about 10 thou oversize on the lathe, six fins will be cut on the mill, it will be heat treated then, finished to size on the tool cutter/grinder.
Here's the rough blank. In this position, the taper will be cut next and I know there will be enough clearance to do the work because the logistics were checked up-front. BTW, this metal is a joy to work on. This was spun at about 850 RPM and 0.004 IPR (left to right cut) with naked carbide TCMT 3251 insert. The insert I used was borderline shot but, the piece has a beautiful finish. It's practically hard to screw-up good quality metal.
We'll continue later... Please be patient because I gimped-up a few fingers and am on light duty these days...
Ray
This metal is a little expensive so I'll want to use as short a piece as possible. To do that, I'll pass along a method of spinning between a 3J chuck and a dead center -and still managing to get perfect concentricity. I'll show step by step and it's useful for folks who prefer not to spin between centers. Normally, I would spin between centers but I'm trying to conserve this piece of stock.
It starts out with this, a hunk of O1 and a CAD drawing with the dimensions of the cutter. The cutting edge diameter goes from 1/2" to 1.1" over a distance of 2.4". I've chosen a 2" long shank to drive it and I'm giving myself a generous extra 1.5" of material for work holding in the chuck and dead center. You should be able to see this in the photo below.
First, lets see how much room there is and if it's even possible in this little space. Here, I'm taking a piece of old brass boat propeller shaft and seeing if there's enough room to work. After thinking things over, I'm going to splurge and cut my piece 7" long instead of 6".
My 3J chuck (just the stock chuck that came with the PM/QMT lathe) is fairly well behaved after some minor tuning and balancing. If your 3J does not re-center well at the same diameter, you should probably switch over to a 4J and scrap your 3J. When a 3J does not re-center at the same diameter, it's got serious problems -probably with the scroll and/or jaw journals.
The trick to this is to always make a mark on the piece and put it in the chuck in the same orientation. Start by facing and drilling one end and making a mark (red spot) that lines-up, in this case, with the insignia on the lathe.
When you've done one side, flip it around and face/drill the other end making sure the mark is lined up with your landmark. Once that is done and without removing the piece after the second face/drill operation, I'm going to reduce the shaft to 1/2". This will later be used to grip the part with the 3J chuck. Note: At this time, we know 2 things for sure. 1) the center hole is concentric with the 1/2" stub 2) the 1/2" stub is concentric with the average outside diameter of the uncut shaft. -We also know that the center hole "should be" pretty well centered with the center hole on the other end. Here's the 1/2" stub:
Now, flip the piece around and grab it in the jaws by the stub. Bring-in your dead center and tighten things down. Make a light pass of about 0.005 DoC. Then measure the shaft left, center and right. On my first pass, I had difference of 0.0046", wide at the tailstock end. This means that the tailstock must be moved toward me by 0.0023".
The next sequence of steps, to move the TS 0.0023", are important to do in the proper order.
First, put a TDI on the end of the part and set it to a zero point (utilizing 1/2 the travel of the TDI). Second, slightly loosen the chuck jaws so they are still grabbing the piece but not loosely. Third, move the TS head by 0.0023". On my new TS, lateral adjustment can be made without unlocking the base from the ways. My finger is pointing to the lateral adjustment on this TS. If you have a traditional TS, making this adjustment may take a little trial and error. Once the adjustment is made, tighten everything backup. In my case, after tightening the chuck, I loosened the TS base slightly and re-applied sufficient dead center pressure. This TS does not lose center when the base is loosened and re-tightened.
And finally, take another pass and re-measure the shaft diameter at left, center and right.
In this particular case, the shaft came out measuring 1.3197" 1.3198 and 1.3199; thus, it is holding +/- 0.0001" -Good enough for this piece because it will be cut to rough form and about 10 thou oversize on the lathe, six fins will be cut on the mill, it will be heat treated then, finished to size on the tool cutter/grinder.
Here's the rough blank. In this position, the taper will be cut next and I know there will be enough clearance to do the work because the logistics were checked up-front. BTW, this metal is a joy to work on. This was spun at about 850 RPM and 0.004 IPR (left to right cut) with naked carbide TCMT 3251 insert. The insert I used was borderline shot but, the piece has a beautiful finish. It's practically hard to screw-up good quality metal.
We'll continue later... Please be patient because I gimped-up a few fingers and am on light duty these days...
Ray
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