• Machine tool reconditioning
• Repair and replacement parts
• Factory trained service
• Training -- operator, set up, or maintenance -- in your facility or ours
• Gear Machine Sales -- We have reconditioned hobbers & sharpeners in stock -- can be seen under power
• Hob sharpening
• Consulting and appraisals

In all cases, F must be evenly divisible by the number of threads on the hob. Multiplier K is the desired number of hob teeth along the helical thread path between the centered tooth and the next tooth to be centered.

HOB SHIFTING FOR LOCATING A PART TOOTH

It is sometimes necessary to locate a part tooth in relation to a detail of the part. Usually, it is an angular location such as the relationship which is held between the crank and the spline for mounting a timing gear on a crankshaft. To maintain the rotational relationship between the hob and the part, the hob must be shifted a whole number of axial pitches.

Since the driven gear on the hob spindle is a helical gear, the hob is rotated independently of the work spindle as the hob is shifted. To compensate for this independent hob rotation, a corrected amount of shift must be used based upon the lead and axial pitch of the hob, and the lead of the hob spindle gear. The correct relationship between the part and the hob may be obtained on successive work loads by shifting the hob according to this formula.

Where S equals the amount of hob shift to maintain rotational relationship with the part and Lh equals the lead of the hob.



Ls equals the lead of hob spindle gear (See table)
T equals the number of threads on the hob
Pn equals normal diametral pitch of the hob
Px equal axial pitch of the hob



La equals the lead angle of the hob.

Use the minus sign if the hob and the hob spindle gear are of the same hand; use the plus sign if the hob and the hob spindle gear are of opposite hands. The lead and hand of the helix of the hob spindle gear can be found in the following table.

After each shift, the position of the generating flats on the part teeth is not the same since the cutting edges of the hob teeth assume a new rotational location. Under these conditions, a hob tooth cannot be centered.

If you have any questions or have a particular topic you would like to see discussed here, please contact us.