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Martindale Chain-Drive Commutator Grinding Tools
Designed at the request of the Railroad Industry, but equally suited
 for grinding commutators of industrial equipment up to 26" long.

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Grinder Sizes
The table below shows stock size Grinders and the length commutator bars they will grind.  Two commutator lengths are given in each case, as two different width Commstones can be used.
Martindale Plain Lathe Type Commstones 1" × 1-1/2" × 6-1/2" and 1" × 2" × 8" in both  Coarse (C) and Fine (F) grades are used.
Extra Coarse (EC grade can be used where the commutator is deeply grooved.  Medium (M) and Extra Fine (EF) grades are also available.

Grinder mounted on Traction Motor
Length: 5-1/2" to 24"
Width: (without handle or knob)
Height: 4-3/4" (base to top of stone-holder nut)
Adjustable Support: 3" (from center of brush-arm hole in lower part to center of joint with upper part)
  * Grinding Lengths:  
Grinder Base Length Using:
1" ×1-1/2"× 6-1/2"
1" × 2" × 8"
Catalog Number
5-1/2" 6" 7" GRDR705
7-1/2" 8" 9" GRDR707
10" 10-1/2" 11-1/2" GRDR710
12" 12-1/2" 13-1/2" GRDR712
14" 14-1/2" 15-1/2" GRDR714
16" 16-1/2" 17-1/2" GRDR716
18" 18-1/2' 19-1/2" GRDR718
20" 20-1/2" 21-1/2" GRDR720
22" 22-1/2" 23-1/2" GRDR722
24" 24-1/2" 25-1/2" GRDR724
* At least 1/2" can be added to grinding lengths be cocking Commstones in the stone-holder.
The Martindale Chain-Drive Commutator Grinder is a departure from previous designs, in that friction has been reduced to a minimum.  Grinding dust has little effect on the operation
Two or three turns of the crank will move the carriage from one end of the bed to the other.  The operator can "feel" the stone cut, and how fast to feed it.  This is probably the quickest and easiest Commutator Grinder to use.

Grinder mounted on a Diesel-Electric Generator.
Supports and Accessories: Catalog Number
Universal Adjustable Support GRDR740
Adjustable Wedge Block GRDR741
Steel Carrying Case for  Grinders under 18" CASE 102
Steel Carrying Case for Grinders over 18" CASE103
Commstones for Above:  
1" × 1-1/2" × 6-1/2" COMMXLS847*
1" × 2" × 8" COMMXLS850*
*When ordering, specify catalog number and grade (i.e. EC, C, M, F, P)
(See Commstone descriptions under (Abrasives / Commstones))
•Grinders up to 7-1/2" base
need 1 support.
•Grinders 10" to 16" base
need 2 supports.
•Grinders 18" to 24" base
need 3 supports.
A Universal Adjustable Support is available for mounting on round brush arms.  This support is in two parts, hinged together.  It can be used as illustrated, with the grinder mounted on the top section and the bottom section adjusted at the desired angle; or the top half van be removed and the grinder mounted directly on the lower part of the support.  Split fiber bushings reduce the clamp from 1-1/8" diam. to 3/8" diam. in 1/8" steps to make a tight fit on the brush stud.
Weights, 5-1/2" base Grinder complete, Net 7 lbs., Shipping 10 lbs., add 1/2 ld. for
each additional inch.

For mounting on a flat brush arms use Adjustable Wedge Block shown in Figure 6, under Commutator Grinding and Turning Tools.  (Use 1, 2, or 3, according to length of base).