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sloppy cope and stick joinery

1/7/14       
RC

So I have been wracking my brain/chasing my tail trying to sleuth what is going on.
Corrugated back cope and stick knives are creating very loose profiles. I have mic'd all grinds on the knife and they are right, and the knives are in the same cutting circle off the table

The procedure we use for installing is setting the head on the shaper table and dropping knives down into corrugations on top other steel knife blanks. I have been using this method for the past 13 yrs on this shaper and only on the past 2 jobs are we getting this result.

Another weird thing (that may point to some other problem)is that the groove in the stiles is tapered down into the bottom .
In other words to fit properly the tenon would need to taper out towards its end. Its hard to describe in words. See attached pic.I am thinking it is some kind of vibration, but the discrepancy is .010!
Thought maybe bent spindle, but it seems to be fine.

Has anyone had this ghost in their machine before?


View higher quality, full size image (2592 X 1936)

1/7/14       #2: sloppy cope and stick joinery ...
joiner Member

Wild guess here. Is it possible your machine shaft is bent and causing a a wee bit of wobble?

1/7/14       #3: sloppy cope and stick joinery ...
Dave

Is it possible your spindle isn't square with the table? You might try a straight edge between some spacers on the spindle and check it.

1/8/14       #4: sloppy cope and stick joinery ...
Russ

RC
It appears the profile has 90 degrees in the design, when re-sharpened they would have had to move the axial on the grinder to sharpen the vertical edge, thus changing the profile making it smaller in overall width of the dado groove.
It only works correct the first time, every time after the initial grind you will have to offset the knives to maintain the proper width of the groove.
In order to maintain the moulding knife correctly you would need to put a draft angle in the design of minimum two degree, this will enable the moulding knife to be sharpened correctly every time without having to offset the knives.

This is a dilemma all craftsmen that need 90 degree grooves are faced with, insert tooling would work best for this application.

I hope that helps explain what I see, maybe others will have more to add.
Contact info on my site if you need it.

1/8/14       #5: sloppy cope and stick joinery ...
Russ

Website: http://www.mirror-reflections.com

There are articles on my website that may help you get a better understanding about moulding knives.
Happy New Year!

1/8/14       #6: sloppy cope and stick joinery ...
Russ

Website: http://www.mirror-reflections.com

Please read article posted below, it the steel when cut was out of square as you may be getting two different reference points on the knives when placing the knives in the cutter head, causing the offset your experiencing making the groove bigger than needed.

Article

1/8/14       #7: sloppy cope and stick joinery ...
Russ

Website: http://www.mirror-reflections.com

RC
Here is a quick way to tell of your knives are offset creating too wide of a groove.
Remove cutter head with installed knives from shaper.
Lay cutter head on table on the rounded side (like you we going to roll it)
Place small straight edge on flat end of cutter head referenced side.
Measure from straight edge with calipers to one edge of the groove cutter.
Repeat procedure on other knife, you should find the offset.
Theory
Knives were out of square when cut, that's not the problem, referencing the knives before the initial grind was done is the problem. The initial reference point was ground away during grinding causing two different reference points on moulding knives.

1/9/14       #8: sloppy cope and stick joinery ...
JeffD

First thing I check is that the knives are in alignment with each other. When you drop and align on the table your trusting that the grinding was accurate and from the same end your bottoming out. Instead use a dial indicator to check the heights of a part of the profile of the knives with the head installed on the machine. I use one with a magnetic base so I can pop it on, check the knives and go!

If you find the knives are perfectly aligned I would then check the spindle for straight and square. Also make sure you have the spindle height locked in place when checking and running. I've found on some machines there's movement when locking the spindle down.

good luck,
JeffD

1/31/14       #10: sloppy cope and stick joinery ...
worwood Member

I have had that problem a few times, and when I did, it was always the bearings. When the machine is running, the bearings also would make more noise. It was like a hum. So I believe it was allowing the spindle to vibrate and wobble. That would be where I would start


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