What's new
What's new

1 1/2 inch per foot taper reamer


Cast Iron
Aug 1, 2006
I need a large tapered reamer for an oversized hole in a pump jack arm, the wrist pin hole, I don't have the arm yet but looked like I would need to be over 2 1/2 inches on the large end and at least 6 inches long. the next question is Tree the only taper boring head and would it do a taper 4 1/2 inches long or are there other manufacturers of taper boring heads.
Pan American Tool has made me custom HSS reamers before and they were good quality, and inexpensive (for a custom reamer)... No idea if they'll make one that big, but can't hurt to ask.
You could pull it off with a Tree head if you had a wide choice of feed rates on your quill. The boring head would only have to move on the radius, while the quill did the axial move. This would require a great deal of coordination to make work. Success would be easier if you could turn the male taper to match the female.

Could you step bore the female taper with fine enough increments the male would pull tight?
This would require a great deal of coordination to make work.
Don’t understand this statement.
The Tree taper boring head generates the tapered bore all by itself.
There is no combining of out and depth feeds to emulate a taper, the head does this as a stand alone accessory.
Just have to set the angle and feed it out at that angle. ( it’s like a facing head where the slide doing the facing is at a set able angle).

Think 4 1/2” depth would be pushing the limits of that head.
...Tree.... taper boring head.... would it do a taper 4 1/2 inches long .

The slide travel is 2" listed.
Not in the shop to see if you get any more for overtravel, but if so, it would not even be 1/8".
Sure, you could probably do it in 3 steps. But the slide is not large nor rigid - with 4-1/2" bar extension to fit down the hole, I'd expect chatter & divergence.

is Tree the only taper boring head .... or are there other manufacturers of taper boring heads.

There is at least one Euro double trunnion head with much more rigidity and range. Not sure it any go 4-1/2". They turn up sometimes on eBay for a few $1,000's. Most of the others that advertise "can do taper bores" depend on a gear ratio between the boring head out-feed, and the mill spindle downfeed.


PS: If you wanted to try the geared approach, a Precision Tool Co Universal might have potential. Use a mill with a geared feed, like BP. Then make up a star-wheel to go in the feed socket for the PTCU with the number of wings corresponding to the necessary cross feed, that would engage a trip-pin added on the rotating part of the tool. Probably take some other method of compounding the reduction, though, for typical acute machine shank tapers. :)
Last edited:
Yes, I'm familiar with how the Tree head is supposed to work. However for the OP's situation the travel is far to short. I would be surprised if the Tree head has 2" of travel going by memory. Travel length is not specified in the instructions. For a smooth continuous taper a Tree head would be used more as a conventional facing head, doing the radial movement, while the quill does the axial movement.

Even resetting the Tree head and doing the bore in 3 segments would be about as bad as step boring the entire length.

Lenz made a couple of different taper boring heads, and Wohlhaupter made a very fragile unit. Neither had enough travel to do the job.

To the OP. I think I'd make it a straight bore and insert a plug. Then rebore the hole to original dimensions.
Find you a lathe with a large enough swing, even a gap bed lathe, to bore the taper in the arm.
I recall seeing pictures of a boring attachment on a horizontal borer that could be set to cut a particular taper in a part.
It would take an eight foot swing on the lathe and a ton of weight to balance it out, I have put in straight pins before and will likely do it this way, it will be a big unit for my BP, well over 500 lbs hanging over the side. I wonder about doing step boring, but to do it in fine enough steps to be useful would be tedious, I think on of the high end facing heads that you can select a feed rate on, then set the feed on the quill down feed would work the best, I could make the pin to fit, but I'm to old to but a high end facing head.
OK, is this an oil well pump jack? My first thought was water and wondering why such a large pin. Your dimensions suggest that would be a whole lot of water.
This is an oilfield pump jack, way to big for lathe or rotary table, an old lodge & Shipley T lathe might work but I don't think the compound can do a 4 1/2 inch taper
If you have something with 5 MT or 50 taper or an HBM, it would be possible to make a plug arbor with an offset to take a slide, such as the old Master slides. Essentially the base of a compound, with an offset to stack the slide & put the bar near center, in the machine spindle with the bar on a toolpost. Set the angle, then set up a star wheel and trip to advance the slide. Slide does have to be offset so the tool point is on center, and tracks a path in parallel plane to the slide.

Not gonna work on a BP, though. There would be a foot sticking out to start, and then 4-1/2" + overtravel when it clears, depending how the bar & TP are arranged.

I almost think this could be piloted, but that's too far to think. :)

Practically, an oversize shop cobbled version of the Tree.
Maybe with a pilot.
Last edited:
A cnc mill with a W axis head is the new version of a Tree (or other taper boring) head. Some are available as a spindle tool. I know Ikegai made a machine with it integral to the spindle.
Hi ronf:
I'd try to find a way to interpolate it on a CNC mill.
Even if you have to hang your part out the door and defeat the door interlocks, you can drill a start hole and then drop down in small increments with a bullnose cutter and it'll be dead nuts accurate when you're done.

Find a shop with a decent sized VMC if you don't have one of your own.
Worst case this job shouldn't take more than half a day or so.
Someone with a big enough mill can probably run it start to finish in an hour.


  • Like
Reactions: pcd
Implmex, using a cnc mill would be great but I'm in Montana and really don't know of one with in a days drive. As far as drilling the hole that is done already, the original pin came loose and has the hole enlarged now, I would take it some place in a heartbeat as it is quit large for my machines, I wish I had a vertical head for my Cincinnati mill, that would help, but at the end of the day I'll fix it and it will another fifty years.
Hi again ronf:
Is there a compelling reason to try to make the wallowed out hole into a properly tapered one?
This is going to be hard and expensive to do no matter how you try to take it on.

Could you just bore it out in several steps to clean it up and then make a step pin for it?

It should do just as well as a tapered pin and socket and it's a bazillion times easier to do.

Something like this you could tackle on a Bridgeport if you needed to, but of course, it would be nicer on a bigger, stouter mill.
If you happen to only have a horizontal mill you have a more complicated fixturing problem, but with enough sheer bloody mindedness you can make it work on a horizontal too.
Turning a custom pin for it is a doddle.


The shafts on the gear boxes on the larger jack pumps are trying to lift a 15,000-foot string of sucker rods and crude oil above the rod pump on a oil well all at the same time, on some of them. They do have counterweights to somewhat balance the load on the gear box. But even with that, that sudden loaded to unloaded and over again, a thousands times a day seven days a week for fifty years, eventually will wear the shaft out and the bore of the crank hub to the condition it is now. I'm exaggerating a little here, pretty close to actual conditions. It don't matter how worn out it is, they want it rebuilt and put back in service yesterday.
Got to thinking, most of the jack pumps I remember being around back in my teenage years, had straight shafts with tapered keys wedged into the keyways to keep the hubs onto the shafts. Of course they were smaller pumps, too.