Homeshop Bagpipe Reamer Building
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Welcome!

This site will be a documentary on the building of reamers for Irish Uilleann bagpipes out of hardenable tool steel...in the home hobby machine shop.


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This is a method for turning an accurate, non-linear taper in CAD defined segments. Without going into the merits of pipe chanter bores with acoustically significant "bumps", (not gonna go into THAT can of worms! ), much of the dimensional data nowday's is in the form of internal diametral points, taken with guages of a known diameter, inserted into bores of instruments with particularly good sound, to a measured depth. This data can be plotted on a CAD program, the points connected by splining, and a graphic reproduction of the bore made. If this plotted line is then broken into .100 long segments, and the intersections diameters are analyzed using the CAD softwares drafting capability...a series of points can be recorded, which when turned in tool steel on a metal lathe, will reproduce the bore.


 




Turning in short segments close to the chuck has some advantages. When a straight taper is turned on centers, with the tailstock offset, deflection (push away) in the unsupported middle of a 14" - 17" long steel noodle will cause inaccuracy, and almost certainly trigger chatter. A follower rest would cure that...but on a taper, that would be problematical. A steady rest could be set up in the middle of the workpiece...but that introduces an interruption. Keeping the work close to the chuck eliminates chatter, and the small mismatches in the steps (typically .001 - .002) are easily filed & polished away.

A word about TIR (total indicator runout). Three jaw universal chucks are usually good to about .003 TIR, 5C collets to about .0005, and soft jaws bored under tension should run dang near as true as the machine's spindle. I would not advise using a 4 jaw independent chuck...due to the large number of diameters to be turned...or unless you're REALLY masochistic. I keep polarity marked, on the workpiece, with a magic marker lined up with the chuck keyhole. If you pull STRAIGHT out, you can keep pretty good concentricity with the segments you've just turned...rotate the reamer blank as it's pulled out & you have introduced an undesirable concentricity stack-up problem.

Regarding tooling...I prefer a sharp, 0. radius, high speed steel (HSS) tool. This is a topic on which I have seen many conflicting opinions. Small lathe's frequently come with carbide insert tooling. This is convenient, the CNC's I program depend on 'em for quick, dimensionally repeatable insert edge indexing. Industry love's 'em...BUT most hobby lathe's are not 5000 pound CNC's, with microinch tolerance ballscrews and massive rigidity. Lathe inserts work using pressure...they are not razor sharp, like a freshly ground HSS tool. This can cause surface finish problems when a deliberately engineered not-to-be-sharp insert exerts pressure against a small lathe carriage with slop in it's fit. If you must use carbide inserts...use one's with a positive rake.

A word about tools...you'll need a good micrometer, although vernier/dial/digital calipers will do...and a 1 inch travel indicator. Because these dimensions are turned in short .100 long segments, a blade mic is optimal for measuring diameters...but a regular mic or caliper's should do fine.

Software: Any CAD program capable of dimensionally analyzing points could easily be used. I used a NURBS (non uniform rational B spline)...(ok, THAT made sense, LOL) spline to connect the points. If you have any misgivings against using a mathematically generated gentle curve to connect the dots, or are just turning a straight taper in short segments...dont use it. Also, don't use a spline in the throat area where you want a straight line for a pilot. When drawing your CAD profile...MAKE SURE you use a DIAMETER setting, not a RADIAL one. Lathes use dia., mills use radial...if you use a radius setting your diameters will be TWICE too big...and the taper will be wrong.


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