Category: "Boring Bars"
A very common concern with any boring bar is that the bar sometimes will not repeat on bored size. This can be caused by one a few different things, or a combination of more than one.
You set your mike and bore a hole and find the hole is oversized, you reset the mike and the next hole is then undersized, obviously there is something that is not right.
First thing we would look for are scores or scratches in the micometer face. If the mike is damaged, the bar will not repeat.The mike should be returned to KW and the face reground and repaired.
Micrometer stem bend, will cause the same problems depending on the amount of bend and the amount of stock to be removed. A quick way to determine if the stem is bent is to insert a feeler gauge (.002) between the face of the mike and the tool bit, then tighten the bit. The feeler gauge should stay in place, and if you slowy rotate the mike in the boring head, the tension in the feeler gauge should not increse or decrease. If it does, the stem is bent and requires replacement.
Another thing to check is if the micrometer not locating into the boring head correctly. The stem of the mike has a V-groove in it which works with a spring loaded ball bearing to insure correct position of the mike into the head every time. If the groove is worn or the ball is out of adjustment, the bar will not repeat on size. The micrometer should "snap" into the head and when slight rearward pressure is applied, the mike should snap back into the boring head. If it does not the ball positon will need to be adjusted. Contact Tech Services for assistance in this case.
If you tighten the tool bit and the tool bit moves away from the feeler gauge, and the feeler becomes loose, there is a different problem. Either the tool gib, tool holder or boring head is worn. You can examine the tool holder quite easily by simply checking the angle where the gib plate contacts the tool holder for visable wear and also feel it for any step. If worn, it will require replacement. You will need to remove the gib from the boring head to examine it for wear also, if the tool holder is worn, it is likely the gib will be worn also.
The boring head can also be worn, and cause the same problem as the tool gib or holder. If the boring head is worn, then the head will need to be replaced. Rebuilding a boring head is only something that the factory can do, and all heads may not be repairable. A combination of two or more of these concerns may be found on the same machine. These findings are normally on very old or high service units.
These are but a few possible causes for potential boring errors in bore size.
As always please contact KW Tech services for further help if required.
From time to time it may become necessary to re-calibrate your boring bar micrometer. Kwik-Way can not calibrate your micrometer here at our facility due to the fact that it must be calibrated to the boring bar that it is used in.
Please follow the the instructions carefully and your micrometer will be re-calibrated and accurate again within minutes.
1. Using a scrap block, center the boring bar to the cylinder to be bored, and tighten the base clamp screw.
2. Raise the boring bar up to allow the tool holder and bit to be installed into the boring head.
3 With the tool holder and bit pushed back into the boring head as far as it will go, tighten the gib set screw. Now lower the boring head until the the tool bit is just into the top of the bore.
4. Loosen the bib screw and allow the tool to carefully come out and contact the cylinerbore. Tighten the gib screw.
5. Raise the boring head to allow the boring bar mike to be inserted into the boring head. NOTE: Have the micrometer adjusted large enough so that the tool bit will not contact the face on insertion.
6. Slowly rotate the micrometer spindle untl the face of the mike JUST touches the tool bit. Now remove the micrometer and advance the reading by .010 to .015, then tighten the micrometer lock screw.
7. Insert the micromenter back into the boring head and loosen the gib set screw to allow the tool bit to contact the face.(Use caution so as no to have the tool bit scratch the face of the micrometer) Tighten the gib set screw.
8. Bore the cylinder.... now measure the actual finished size. DO NOT loosen or remove the boring bar. Take the measurement with the bar in place.
9. Place the stem of the boring bar micrometer into a vise with soft jaws so as not to damage the stem. Loosen the allen set screw found in the rear os the mike thimble in the knurled area.
10. Carefully rotate the thimble so that the mike now reads your bore size. Tighten the set screw.
11. Now loosen the micrometer lock screw and rotate the thimble either clockwise or counter clockwise, whichever direction is closer to thimble "0". Now re-tighten the micrometr lock screw at "0". If necessary, loosen the thimble set screw and slip the thimble up or down until the 0 is on the appropriate black line on the body of the micrometer then tighten the thimble set screw.
12. Loosen the micrometer lock screw and rotate the thimble to the reading of the bore size in your test cylinder. Now add .010 to the reading and rebore the cylinder. Measure the cylinder to verify size, fine tune your micrometer reading if necessary.