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Problem with knife on W&H10/17
The problem we're having is when cutting arched planton frames on our Williams & Hussey, the knife is digging into the inside of the arch when run through the correct direction. If we feed it through backwards, it doesn't dig in, but it does break a lot of the arches. Does anyone have any suggestions? The knives are ground in a Weinig Powermat head, could the diameter difference of the Weinig head and the W&H be the issue? I've ground 1 of the 2 knives slightly wider than the other to assure that they don't get set up offset.
I've attached some pictures. Notice the red arrow on the pic of the full frame, that's where they are breaking off.
I forgot to mention, the profile is a half round 3/8" thick 1" wide.
My first thought is that you are not controlling the work piece completely as it passes through. Can you provide a picture of the fixture that you are using? The angle of the cutting tool can also contribute to what I see. What is the hook angle of the head and at what grinding angle are you preparing the tool?
Dr. David Rankin
Good morning Dave!
The fixture he's using is the 2 bearings on 1 side, and one on the other that came with the machine. Due to the fact that the shape is more of an elliptical, it's pretty much impossible to put anything else on it.
Hook angle on the head used to grind the knives was a 20°. We do have a 12° here I can use. Back grind angle is 30° and finish angle is 20° and side clearance is 15°.
Do you or anyone else know if there's an adapter available for the Weinig R960 HSK for grinding W&H knives? We've never had this issue before and have always ground the knives on our grinder in the moulder heads, but this is the first time we've done a profile that the knife cuts the complete profile all the way down to the width.
A combination of different hook angles and diameters of the cutterheads on a half round circle may be the issue in my opinion.
We're finished running the job by feeding the pieces backwards, just had to make extra to make up for the broken ones.
Russ, the knives are corrugated. Maybe next time I'll grind them in a 15° head and see if it helps. The diameter of the heads is 90mm, so a little smaller than the ones you use. I was thinking that that was the problem, but if you're using a larger head, it probably isn't, which would lead back to hook angle being the likely culprit.
Is the head you use designed to grind W&H knives, or is it just a regular moulder head? 122mm sounds like it's just a standard spindle head, but is the hook angle special to W&H or is it just what you use normally? I do have a spindle adapter and a 20° 122mm head I could try using next time.
Thanks for your time!
Is this the head you are using?
We have had this issue before on a poplar symmetrical profile we use that's similar to your PO 1.500"-17 where the top half round ends, but only when making certain radii. Maybe picking up that head would assure no (or at least fewer) future issues.
I'm really shocked you have not run into this before. I would assume anytime you try and take a partial side cut on an arched moulding you would run into this. If the part is not fed perfectly perpendicular to the face of the tool the tool it would act as if it were narrow.
There are really only two things I've run into over the years we've been running our curves on the WH that cause this problem.
First is the depth of the knife on the inside of the cut. As the wood curves under the WH head the overly deep steel will hit the wood on both the downswing and subsequent upswing of the knives either side of on-center with the low point of the cutter head swing. This causes the scalping you see on the inside of the profile. The solution is to grind a little steel off the point of the knives and then do some hand sanding or separate round over router bit cutting to bring the profile back to final design.
With that being said though if you are grinding the knives on the wrong head then you could be causing the problem by having the steel too deep for the WH. The length from the deepest cut into the steel to the back of the knife needs to be 1 1/2" on the WH. If your setup is resulting in this being greater than 1 1/2" then that is increasing the likelihood of scalping.
While this discussion has spent a good deal of time reviewing the hook angle of the knives I don't think this is the problem unless an incorrect hook angle is contributing to the steel's deep cut to shoulder length being greater than 1 1/2".
The other problem that can cause this is the 3-point bearing guide system being off center from the low point of the cutter head swing. The proper center alignment of the 3-point bearing support is not directly under the center of the cutter head. Rather it is about 1/2" to 1" towards the out feed side of the machine, at the low point of the swing of the steel.
While I will usually look to an overly deep cut on a tight radius as the root of the problem in your case I'd say it's an off centering of the 3-point bearing pinch. That would explain why you get the scalping when feeding normally but don't get it when hand pushing the wood backwards through the machine (we've done this too occasionally over the years on chippy wood). By pushing the wood through from the out feed side you are most likely forcing it slightly off center of your 3-point bearing pinch, and more on-center with where it needs to be under the cutter head.
I took your comment that you were running the mouldings "backwards" through the machine to mean you were feeding them in from the out feed side. I say you are hand feeding because I can't imagine how you could make the cutter head run in the correct direction while getting the feed rollers to run in reverse. If you've managed to sort that out I'd love to see how you pulled it off.