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Grinding Custom Spindle Moulder Knives

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Grinding Custom Spindle Moulder Knives

Postby Trevanion » 04 Oct 2020, 12:54

Some time ago I made some knives for performing the cross-grain cut on some sash horns and I thought I'd share the process here.

It started with the really rough shape of the horn shape in question on a piece of hardwood, the full length of the horn is 60mm so a 50mm knife won't do it all in one pass and 60mm knives aren't available so I'll just have to make do. (Whitehill do 55mm blanks but they're twice the price of 50mm)

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The block is then split with a 25-degree cut which will give you the template with the cutting angle included, so there's no guesswork or offering up to the workpiece constantly, just grind to the line.

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25 degree piece laid sawn face down onto the cutter to give the correct profile and is then marked with a scribe onto black sharpie.

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Most of the waste is cut away with an angle grinder.

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Cutter is then ground at 90 degrees to the line with a 12mm wheel with a radius.

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The second knife is then marked off the first knife to get them perfectly matching, you could use a couple of 6mm drill bits to align them but I just eyeballed it.

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The bevel is then ground onto the knives just until the 90-degree portion disappears and the knife becomes sharp, the bevel I copied off an existing knife.

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Cutters are fitted to a Euro Block (I will be using a heavier, larger steel one for the actual cutting for more support behind the knife) with blank limiters and a test cut is made with a scrap screwed to an end of a board.

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Perfect match :). £10 of cutter knives and 1 hour of time which I kept an eye on, I probably would've spent more time drawing it up to send it to Whitehill (Of which I would then have to wait for correspondence and the knives in the post) than actually grinding it myself.

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68 Sash Stiles ready for moulding the horns.

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A very real bodgers delight method of holding the sashes! :lol: Worked very well actually! It could hold up to 6 at a time, no vibration, slop or anything like that going through the cutters. Of course, in future, it will be nice to have a jig that's got better ways to hold it and perhaps looks a bit sturdier.

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from the inside, Xs marked on the sides of the sashes that need the horn on so that they go together the right way around.

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68 stiles moulded in less than 30 minutes without being out of breath, no joke.

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The surface finish leaves a little to be desired for, on account of using chip-board in the jig which seemed to have steel strands in the mixture which I could see sparking as I plunged it through it. Next time I will use softwood ends instead and touch up the cutters. It's still a very good cut surface across the grain on Accoya though, very little hand sanding and it's up to very good standard. The end-grain feels like glass, it's buttery smooth.

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In all, probably saved at least a day and a half of cutting horns on the bandsaw, sanding them all and making them good. In the time it took to cut four horns perfectly on the moulder I would've only sawn one horn to rough shape, and I probably would've burned up a bandsaw blade too cutting all 68. It was worth doing, they're all consistent and perfect now.
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Re: Grinding Custom Spindle Moulder Knives

Postby wallace » 04 Oct 2020, 13:25

I thought when you grind cutters you dont actually use the desired shape as a template. I've seen in books where some kind of projected drawing is used to find the shape needed on the cutting edge.
I've seen a gismo that Robinson made for creating the desired cutters, its all very complicated and reminds me a tech drawing back at school
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Re: Grinding Custom Spindle Moulder Knives

Postby Trevanion » 04 Oct 2020, 13:45

wallace wrote:I thought when you grind cutters you dont actually use the desired shape as a template. I've seen in books where some kind of projected drawing is used to find the shape needed on the cutting edge.
I've seen a gismo that Robinson made for creating the desired cutters, its all very complicated and reminds me a tech drawing back at school


No, you wouldn't use the profile to draw the template with the end cut at 90-degrees square-on because this will give you the wrong shape for the cutting angle of the knife, by cutting the desired profile with a 25-degree angle you can use this as the template for the cutting edge as it will be very close to the shape required to perform the cut when using a euro block.

I've never tried developing a profile the old-fashioned way by drawing out the cutter block and the profile 1:1 on a piece of paper, I've got an excellent book that details this process though, "Practical Geometry for Carpenters, Joiners and Woodworking Machinists" by A.B. Emary and I may give it a go next time I need something a bit more complicated.
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Re: Grinding Custom Spindle Moulder Knives

Postby Mike G » 04 Oct 2020, 14:12

I'd have never imagined that horns would be cut on a spindle moulder. Interesting.
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Re: Grinding Custom Spindle Moulder Knives

Postby Trevanion » 04 Oct 2020, 14:42

Mike G wrote:I'd have never imagined that horns would be cut on a spindle moulder. Interesting.


Modern thinking! :lol:

Looking at Cassell's Carpentry and Joinery they actually would've been done in a very similar fashion a hundred years ago, just clamped together flat on a bench with moulding planes instead of clamped together vertical on a spindle moulder. They even used a spelch block to keep the end from breaking out!

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