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Custom shaper Knives Protruding Slightly Above Head

10/15/16       
V Member

Please see attached photo describing my question..

I have been learning to custom grind shaper knives lately. Simply hand grinding to custom templates. I am using M2 1/4" steel and a steel 3" tall x 3.5" diam. cutter head.

I have read that it is not advisable to protrude the knife above the head, but am wondering why? If I was able to, I could custom grind my own panel raising profiles to lay the stock flat on the table rather than against the fence.

Has anyone seen or heard of this setup? I would assume it is perfectly safe as far as breakage is concerned, and that the guideline is simply the manufacturer trying to avoid liability for people extending the blade much further than this.

Thoughts?


View higher quality, full size image (1596 X 749)

10/15/16       #2: Custom shaper Knives Protruding Sli ...
Pete D

Based on your image the projection above the cutter head wouldn't be the issue. The concern would be how far out the knife projects from the side unsupported. I've done exactly what you're trying to do, the difference is I had knives ground for a 3/4"x8" coping disc so more of the knife was supported where it projects from the side. I can post an image when I get back to my shop. I'm sure Someone with more expertise on knife grinding guidelines will chime in, but you might want to consider going with thicker corrugated stock, like 5/16".

10/15/16       #3: Custom shaper Knives Protruding Sli ...
D Brown

Typically the profiled part of the knives protrude beyond the collar or head not above.
If you ground a knife with the RP profile oriented to cut the panel face up and make the knife long enough it works fine .
In my experience face up produces the most consistent panels to fit your groove , even if there is a slight difference in panel thickness they will all fit .
I have been grinding knives for my own use for 30 years or so and honestly the RP is nothing I'd recommend , why not use a safer cutter , maybe one piece 3 wing .

10/15/16       #4: Custom shaper Knives Protruding Sli ...
V Member

Pete D:

I did not show it or draw to scale, but the knife protrusion beyond the head would NOT exceed 3x the knife thickness, or 3/4". Having the cutting edge above the head slightly was wanted for exactly this reason; to get away with a wider profile while not violating the 3x width protrusion. I thought this would open up a lot of options while keeping all of my steel stock 1/4". Even if I did go to 5/16" thick stock, I could still only do 15/16" to the side, which is not enough for most RP profiles.

D Brown:

Is there a specific reason you know of to avoid protruding above the top or bottom of a custom head like this?

Also, I had not thought about running panels face up. I always thought that panel thickness variation would cause fit issues. You say that this is not a problem.. Is the benefit less chatter?

10/15/16       #5: Custom shaper Knives Protruding Sli ...
Pete D

This is the 8" coping disc & knives. I bought the coping discs for long tenons and used the profiled knives to experiment with extra deep cove in panels for passage doors.


View higher quality, full size image (3024 X 3024)

10/15/16       #6: Custom shaper Knives Protruding Sli ...
V Member

Pete D, that looks very nice! Where was this head purchased?

Also, I see that you have the knife protruding just a bit above the head, as I was asking about.

I am guessing my biggest concern will be (if using my taller 3' head) to switch to a top up RP cut so that there will be less side stress on the spindle.

10/15/16       #7: Custom shaper Knives Protruding Sli ...
Pete D

I had forgotten, that disc is actually 9" and has a cutting depth of ~3.75-4" with the knife projection. That's a dangerous cut, I was pushing the envelope with that one and don't recommend trying it unless you have a massive shaper & feeder and going very slowly. I posted the image so you could see an example of a corrugated knife using the top edge to cut with. I can run that head in forward or reverse depending on how I want to feed the panel...face up or down. Those are coping discs sold by CGG Schmidt and I believe they've got 7"/8"/9". They're not inexpensive and unless you simply want to grind your own knives and experiment with profiles, I think D Brown's suggestion of the fixed three wing cutters is a good one. Would also agree that keeping the cutting forces lower on the spindle is always a good practice.

10/15/16       #8: Custom shaper Knives Protruding Sli ...
Russ

Website: http://www.mr-moulding-knives.com

V
I have attached a link to some options that might work better than what you are currently illustrating.

I agree with what D Brown is suggesting a 3 wing raised panel cutter head.

FYI: when you purchase the steel make sure the corrugations go all the way to the top of the steel so you can lock in the cutter head correctly. Some wider steels have a smooth flat surface before the corrugations begins, this would be an issue.

All the best
Russ @ MR

http://www.cggschmidt.com/store/the_innovators.php

10/15/16       #9: Custom shaper Knives Protruding Sli ...
V Member

Russ:

Thank you for the link..

I have already been buying my steel and head from them over the phone! I did not know about this option..

For the cost $270, and $60 for blank knives, this is a no brainer over trying to do something that is not advised.

I will get the jr, as I am just getting started with all this, and only do (and plan to do) up to small kitchen jobs as far as cabinetry goes. I have a 3 hp Grizzly shaper.

Thanks again everyone.

10/15/16       #10: Custom shaper Knives Protruding Sli ...
Pete D

Glad Russ guided you to the right cutter head. The coping discs are too big for a 3hp 3/4" spindle and aren't designed for raised panels. I adapted mine for the extra long cove cut I couldn't get with a standard size panel raising cutter head. Here's a good article and video on knife grinding:

http://www.thisiscarpentry.com/2010/11/26/grinding-custom-shaper-kniv
es/

10/18/16       #11: Custom shaper Knives Protruding Sli ...
JeffD

I bought an Innovator head several years ago and it's been great for doing raised panels. Being able to grind your own knives is handy. However being able to order a fairly good variety of patterns off-the-shelf is the real benefit for me. Plus you can get them in carbide which is great if you do mdf panels as I do occasionally.

good luck,
JeffD


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