Dead true centerdrilling.
I used to work in a gear shop and had to repair gear shafts that had been
centerdrilled and had more then the .001 runout that the print called for. I used a steadyrest with ball bearing rollers and that gave me dead true runout. It is best to collet or chuck on a small part of shaft and let the steadyrest pull the shaft to dead true. Then I hand ground a 30 degree angled tool to form one side of the centered part. Imagine half of a centerdrill without the drill part in front of the angle. If you blue up the center of the part you can see it cut the high point of the runout till it is dead on. Jim |
Dead true centerdrilling.
" Jim Sehr" wrote in message ... I used to work in a gear shop and had to repair gear shafts that had been centerdrilled and had more then the .001 runout that the print called for. I used a steadyrest with ball bearing rollers and that gave me dead true runout. It is best to collet or chuck on a small part of shaft and let the steadyrest pull the shaft to dead true. Then I hand ground a 30 degree angled tool to form one side of the centered part. Imagine half of a centerdrill without the drill part in front of the angle. If you blue up the center of the part you can see it cut the high point of the runout till it is dead on. Jim I agree with you. Boring with the use of a steady rest is an intrinsically accurate operation. |
Dead true centerdrilling.
On Thu, 8 Jul 2004 20:06:39 -0700, " Jim Sehr"
wrote: I used to work in a gear shop and had to repair gear shafts that had been centerdrilled and had more then the .001 runout that the print called for. I used a steadyrest with ball bearing rollers and that gave me dead true runout. It is best to collet or chuck on a small part of shaft and let the steadyrest pull the shaft to dead true. Then I hand ground a 30 degree angled tool to form one side of the centered part. Imagine half of a centerdrill without the drill part in front of the angle. If you blue up the center of the part you can see it cut the high point of the runout till it is dead on. In the last year or so we've had to recenter several inspection arbors. Basically the same, except after putting in the steady rest, we indicated the compound to 30 deg., then ground with a Precice grinder, small CBN wheel. Used the normal bronze against the arbor, gives less runout than BB would. Lennie the Lurker |
Dead true centerdrilling.
How small a centerdrill could you grind?
Jim wrote in message ... On Thu, 8 Jul 2004 20:06:39 -0700, " Jim Sehr" wrote: I used to work in a gear shop and had to repair gear shafts that had been centerdrilled and had more then the .001 runout that the print called for. I used a steadyrest with ball bearing rollers and that gave me dead true runout. It is best to collet or chuck on a small part of shaft and let the steadyrest pull the shaft to dead true. Then I hand ground a 30 degree angled tool to form one side of the centered part. Imagine half of a centerdrill without the drill part in front of the angle. If you blue up the center of the part you can see it cut the high point of the runout till it is dead on. In the last year or so we've had to recenter several inspection arbors. Basically the same, except after putting in the steady rest, we indicated the compound to 30 deg., then ground with a Precice grinder, small CBN wheel. Used the normal bronze against the arbor, gives less runout than BB would. Lennie the Lurker |
Dead true centerdrilling.
Using a 1/8" wheel, the pilot hole was the controling factor. As they
were already in, we could do those with a 5/32" pilot hole without problems, but have also re-drilled the pilot and reground the entire center when needed. IT's not an ideal solution, depending on the condition of the diameter in the steady rest, it may come in to tolerance, in our case .0002", or it may not. If the arbors were an off the shelf item, buying new probably would have made more sense. Some came in to nothing detectable with a .0001" indicator, others would not come in to less than .001". I would imagine that using a tiny point, and with enough rpm to turn it, doing very small centers would be possible, not that I would want to be the one to do them. PITA as it is. On Thu, 8 Jul 2004 21:36:44 -0700, " Jim Sehr" wrote: How small a centerdrill could you grind? Jim wrote in message .. . On Thu, 8 Jul 2004 20:06:39 -0700, " Jim Sehr" wrote: I used to work in a gear shop and had to repair gear shafts that had been centerdrilled and had more then the .001 runout that the print called for. I used a steadyrest with ball bearing rollers and that gave me dead true runout. It is best to collet or chuck on a small part of shaft and let the steadyrest pull the shaft to dead true. Then I hand ground a 30 degree angled tool to form one side of the centered part. Imagine half of a centerdrill without the drill part in front of the angle. If you blue up the center of the part you can see it cut the high point of the runout till it is dead on. In the last year or so we've had to recenter several inspection arbors. Basically the same, except after putting in the steady rest, we indicated the compound to 30 deg., then ground with a Precice grinder, small CBN wheel. Used the normal bronze against the arbor, gives less runout than BB would. Lennie the Lurker Lennie the Lurker |
Dead true centerdrilling.
On Fri, 09 Jul 2004 12:18:15 -0300, Machineman
wrote: In manufacturing they use a center hole grinder, lots of different models available, here is one I found on a search http://www.machineryvalues.com/xdetails.cfm/QN/126727 Not overly complex, usually a dead center, steady rest and a cone wheel grinding wheel. But if refurbishing a center in a shop the above practice is the way to go. Time for some massive snippage her The machine shown, I've seen them in Case, is more used in a production setting, used between heat treating and the final grind ops. More to take care of any nicks or dings and any possible distortion that happend in heat treating. (The V block and destaco clamp sorta give this away.) Beyond that point, concentricity is held from the center, which for production is probably the only practical way. I picked up the "steady rest and tool post grinder" method from watching the machinists regrind centers on some very expensive splined inspection arbors. These arbors were all made with a stub on the end, hardened and ground, which I assume was ground to be concentric with the spline PD and the center from which the spline had been cut. I would have loved to see how they set up the hobber to make these arbors, .004" taper over 12" of length, probably some tolerance on the PD, but almost nothing for helix. I assume there was some grinding of the spline after HT, but have no idea of how that would have been done, don't think I want to, either. Lennie the Lurker |
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