Troubleshooting Uneven Pitch Marks from a Jointer
Pros suggest possible fixes for a jointer that's creating uneven pitch marks on lumber. May 18, 2010
I'm running an old (about 20 years old) Wadkin xjs 6 head moulder. I am using 230mm hydro wedge type blocks (6 and 8 knife) with feed speeds ranging from 30-70mpm. This is a jointed machine. I am experiencing a range of problems with the finish, the most common being uneven pitch (cutter) marks on the horizontal heads. Does anyone have experience with these machines?
(Solid Wood Machining Forum)
From contributor R:
For the amount of knives you have in your cutterhead, your speed should be about 180 feed per minute or more. Try 3 knives in the cutter head if you have a six wing cutterhead or 4 knives if you have an 8 wing cutterhead. Try to maintain 75 - 120 feet per minute feed rates. General rule - 30fpm per knife finishing.
From contributor C:
Uneven pitch marks as opposed to uniform ones can be a sign of something beyond the number of the knives being jointed.
It could be one or more of many things:
Uneven balance of the knives.
Wear of the bearings on the spindles.
Wear of the dovetail slides on the horizontal head adjustment.
Wear marks or dust/woodchips between the reference face of the spindle and the cutter heads.
Worn or damaged drive belts.
Hold down pressures not set correctly or the springs on them seizing up.
The feed unit not feeding smoothly.
There is sure to be more.
It becomes a process of elimination to nail the solution down.
From the original questioner:
Thank you. I have already reduced some of the cutterblocks from 8 to 4 knife. Some of the mouldings done on this machine have been reduced from 6 to 3 knives per block. I am in the process of having blocks rebalanced. I have pretty much eliminated the blocks themselves as the problem. I was considering changing the cutting angle on my straight knife and profile grinders. I have also had extensive work done on the machine re-aligning beds, fences, jointers, spindles and pressure pads. Spindle and outboard bearings are relatively new. The drive belts are the old fashioned V shape as opposed to the more common newer flat belts and pulleys. The problem with the uneven pitch marks is similar to the effect of overcutting (too many knives for feed speed) but the pitch is around 1.5 to 2mm with spindle speed of 6000rpm. Conversations with current and ex-engineers have highlighted an inherent problem with this particular make and model (Wadkin xjs around 20 years old).
From contributor J:
Do you hear a vibration when this occurs? Is it constant or periodic?
From David Rankin, forum technical advisor:
My experience with this model has presented the following areas of discovery.
1. Adjusting tails not parallel and tensioned to maintain a parallel spindle to the table allows for vibration.
2. Worn pulleys or belts. The V-groove in the pulleys can wear and this can cause a poor finish.
3. Loose clamping areas around the spindle occurs when the casting wears, caused by running the machine in an unlocked condition or years of use.
4. Improper lubrication of the spindle bearings.
From contributor A:
One thing you may want to play with is the hardness of your jointing stones. The harder a stone is, the less forgiving it is when applying the joint. Older machines' jointing mechanisms can be stickier or have more slop in them. Changing to a softer stone can compensate somewhat for these issues. Another interesting test is to use a black sharpie and run it along the cutting edge of a fresh set of blades to be sharpened. Then apply your joint to the knives. After the head stops, take a light and examine the heel produced on each knife. Make sure every knife has been hit and that the heels are all relatively the same size. Too big a heel on one or more knives can mess up a joint. It can indicate bad bearings or profile grinding that is too uneven.