Smooth-back moulding head set-up

      Ideas for setting up an older, smooth-back type moulding head. June 14, 2000

Q.
I have several questions.

What is the proper procedure for setting up an older, smooth-back moulding head? Since there are no corrugations should I use a gauge block under the knives to set knife height consistent and if so, will I be able to get it out after tightening gib bolts? Or, do you use some type of gauge, like the ones used for planer knives? If so, what type do you recommend for a 2.5-inch-wide head?

On the type we have, the indicator will only travel about .5 inch in the middle of the knife before the legs will fall off the side of the head. Is that enough to determine if the knife is set parallel? Should the knives be weighted and balanced before grinding? Is there a tool available with a socket head for the old, four-sided gib bolt heads that would enable you to access them in a hole or recess? I am currently using a 3/8 extension, upside-down, with a wrench.

Also:

On an existing 12-inch jointer with a hook angle of 25 degrees, I'm having problems with hardwoods. I know that's too much hook for hardwoods but I'm stuck with it. Is there anything I can do to help? What knife bevel would you recommend to get as much scraping action as possible without back clearance problems?

A.
First, the safety issues must be looked at. Flat-back steel must not be run on machines over 3600 RPM. The steel must not project out of the head body by more than three times its thickness.

I suggest glass bead blasting the knife to provide a better hold in the pocket. I use a long 3/8-inch ratchet drive or torque wrench to tighten the knives. Be sure to tighten them equally. Contact the manufacturer of the head or the sales company that sold the knife stock for proper torque of the screws. The wrench is available from sources including DML and MSI.

To easily align the knife in the head, most people use a simple set-up stand. It consists of a spindle and a flip-down metal plate that has a stop, level to the center of the spindle. By marking on masking tape, the knife can be checked for square. Once the first knife is correct, the others are aligned to the pencil mark made off of the first.

Balance the knives before grinding; this will save you several extra steps that are repeats. Cut the stock, square the knives on both cut edges and make sure all are the same length, balance, and insert into head. Grind and go.

Regarding the jointer:

For hardwoods, a hook angle of 12 degrees or so would be best. If you must use a 25-degree hook, grind the knives at 20-degree back clearance and a 10-degree side clearance. A secondary grind at 18 degrees, only 1/64 wide, would increase the life of the tool.

Another option is to use carbide, and grind it at a 12-degree back clearance. This will give you more of a scraping action and reduce the problem, but will not eliminate it.
Dave Rankin, forum moderator



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