Aligning and old part to a new shaft with a tapered pin
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  1. #1
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    Default Aligning and old part to a new shaft with a tapered pin

    It must be a common problem, but i couldn't come up with the proper word search for the archives so i'll risk re-plowing old ground...

    Assume you're rebuilding an old machine and have a part (collar, gear or handle) that fits on a shaft and aligns and is held in place via a tapered pin. Now assume the shaft is damaged and it's cheaper and easier to replace the shaft than repair it.

    Is there a trick or technique to drill an ream the shaft such that it properly aligns with the existing tapered hole in the original part? From what i've been able to determine, the original part and shaft were drilled and reamed as one. Is the only option to drill and ream the old part with the new shaft as was done originally?

    Mark

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    Set the handle up in your mill vise so that a straight rod added:[held in a drill chuck on the mill] passes through the existing hole, centered on the hole both top and bottom.

    Install the shaft into the handle, and use an end mill to start the hole in the shaft. Finish up with a drill the size of the small end of the hole.

    The use a taper pin reamer to open the shaft hole and take just a squizz off the inside of the handle hole(s).

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    Yes. Mount the old part on the shaft with loctite or similar, then using a drill the same size as the small end of the large hole on the old part, spot drill the shaft. Then you finish drilling the hole with a drill that's just a bit smaller the small end of the taper pin.

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    I have a lot of experience with this, repairing and restoring my Deckel FP2 mill, which has dozens of taper pins. Here is my method:

    (1) Put old part on new shaft. Mark each end of the hole right in the center. I typically use a set of center-point marking rods which I have in both metric and imperial sizes.

    (2) Use a center-punch to get drill start marks at each end, where the hole will enter and where it will exit.

    (3) Turn a short piece of 6mm or 1/4" round steel stock (say 50mm/2" long) with a 60-degree or 90 degree sharp point at the end.

    (4) Clamp that piece of stock vertically in a mill vise, point up. Center the axis of the vertical spindle directly over the point.

    (5) Now rest one center-punch dimple of the shaft on the lower sharp point, and drill through most of the way from the top, using the other center-punch dimple to guide the bit in. You'll be holding the shaft in your hand while doing this. Then flip the shaft and finish from the other side. Your drill should be about 0.5mm = 0.020" smaller than the (smallest) hole diameter.

    Note: if the dimple mark is far from center, use a center drill or spotting drill to enlarge your punch mark before using a regular drill. Otherwise the drill bit might slip out of the center-punched spot.

    This ensures that your hole in the shaft is correctly aligned with the other part, both on the entrance and the exit side.

    Finally, use a taper reamer to open the hole out with the part mounted on the shaft. A spiral reamer in a battery-operated electric drill works real well. Slobber on some cutting oil and go slow or you'll cut off more material than you expect.

    Here's a photo of the setup. This is on a drill press because at the time I was working on the FP2. Since I didn't have a good way to center the vertical spindle over the point, I drilled a hole in the aluminium scrap, and then used that hole to hold my lower "round pin with a point" support.

    Last edited by ballen; 02-19-2021 at 05:51 PM.

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    Really depends if the hole was centered in the shaft to begin with.If centered then just put together and center the shaft and drill the big end with small end drill. However I have only ran into one group of machines where all the pins were centered, most are hand drilled and reamed. Also depends if they are metric or American. The metric pins are measured from the small end and are available in various lengths so I keep the longest avail in each size. Metric are 50:1 taper and American are 48:1. You also have to find what number it is to get the size(American).
    If it is hand drilled and you can get the female part in the mill then just chuck up the correct reamer and use that to align the part and do as awander said above.

    I have to do a lot of them on the mostly European machines we have. So I have a lot of short round stock that is drilled and reamed for different sizes to hold in the lathe to cut for size and thread if needed.

    I use lh spiral rh cut machine reamers mostly but have strait flute hand reamers also(they cut a little more freely)

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    Thanks Guys. The machine in question is a Monarch 16 CY lathe from 1941. The parts in question are the main feed rod and the mating drive gear. The existing feed rod is worn and bent and 1" dia keyed stock is readily available in the necessary length for a reasonable cost.

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    I would take your part that fits over your damaged shaft, and drive a taper pin through it solidly. Then turn it and bore it until you can't see there was a hole. Now start over. Put the part over the shaft and hold it in place, step drill and taper ream and drive in a whole new taper pin.

    metalmagpie

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    Drill and tap the old part say 1/4". Fasten it in the correct place with a grub screw. Then using full size drill, drill back from either end using the existing holes about 1/8" deep. Pilot drill with a smaller drill from both ends CAREFULLY so your holes meet roughly in the middle of the shaft. Drill back right through from the small end with your reamer drill. That drill normally follows the pilot hole. Ream the hole and fit your taper pin. It worked for me on lots of occasions on site when I didn't have access to milling machines, pillar drills etc etc.

    Leave the pin proud about 1/8" at both ends. Stamp the head end HD on either side of the pin head like this - H O D with letter stamps.

    Regards Tyrone.

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    I like to finish shaft making between centers with having all IDs and Ods running near-dead true.
    Sometimes that can be a lot of work, even 4 jawing one end and the out end in a steady.


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