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Thread: Cutting and drilling rockwell 60
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22nd January 2009, 07:36 PM #1
Cutting and drilling rockwell 60
Hi guys,
I want to modify the riving knife on my minimax panel saw. Presently, the knife sits about 8mm above the top of blade, which is an issue for me. I want to cut the knife down to 2mm below the top of blade, and then drill 2 x8mm holes to re-mount the guard on to the knife. Hardness???...... well a file won't touch it, so I assume the knife is as hard as a blade, which I believe to be around Rockwell 60. Not having machined/drilled etc anything that hard before, I thought I would ask for advice before hacking in and stuffing up a good riving knife. Any advice on cutting and drilling for the modification would be greatly appreciated.
Fossil
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22nd January 2009 07:36 PM # ADSGoogle Adsense Advertisement
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22nd January 2009, 08:14 PM #2
Get a piece of 8mm copper tube or brass tube about 50 or 60mm long. Carefully hacksaw a cross on one end about 3mm deep. The wall thickness needs to be about 1mm. Mount the tube in the drill press with the cuts downward. Build a "coffer dam" around the area where you want the hole with a thick 5/8" washer or similar. clamp the blade down when it's aligned and pour into the "dam" some lapping paste or a mixture of grinding grit and thin oil, eg, diesel works really well. Bring the "drill tube" down into the grit and press down firmly but not so hard that the end is distorted. Spin the drill at about 150 or 200 rpms and gently touch the tube onto the blade. Raise and lower the "drill tube" onto the blade. A groove will be ground out leaving a "slug" in the tube.
This works by a grinding process called "Lapping". The hard grit is embedded into the soft "drill tube" and then it cuts a groove into the hard metal. You can vary the speed to find a suitable rpm that will cut reasonably quickly. Keep in mind that this is a fairly slow way to do the job but it does work and wont wreck the blade from pressure like trying to use a carbide drill. because the blade is so hard, you could also use a "drill tube" made from free cutting leaded mild steel. If you can get it, use the leaded steel for the "drill tube". Use a grinding grit of aluminium oxide of 80 grit size. keep the grit and oil up in the "well" but the main thing is to have patience, you will get there. There are other ways to do this but you risk shattering the blade. Laying a few sheets of newspaper under the blade will help keep the pressure even.
Kody
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22nd January 2009, 10:43 PM #3
It depends how the riving knife is mounted to your saw arbor. If it is bolted on through slots then you can elongate them to allow the knife to sit 10mm lower. this would preserve the upper surface with its existing guard mounting holes.
To elongate the slots you'll need to anneal the area (carefully). One way is to chuck a rod into a drill press and bear down on the area you want to soften. The friction will quickly cause colour change...blue would be soft enough to cut with more conventional tools.
Otherwise use a die grinder or dremel tool to grind the slot longer.
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23rd January 2009, 07:30 AM #4
Thanks for the replies guys.
It depends how the riving knife is mounted to your saw arbor. If it is bolted on through slots then you can elongate them to allow the knife to sit 10mm lower. this would preserve the upper surface with its existing guard mounting holes.
I have attached a couple of photos to give a clearer picture of the situation.
I can't lower the knife because it will then foul on the blade, unless I carve out the slot laterally quite a bit. That is why I was considering cutting from the top and then re- drilling the knife.
Any ideas on cutting methods?
Kody.... I do have a few offcuts of 25mm leaded steel round bar, so I can turn up a tool and give your suggestion a try for the holes.
Thanks again.
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23rd January 2009, 07:39 AM #5
Another question..... Kody, I have an old alox 80 grit wheel that is worn down to 4" diameter. If I crush it up and use the grit, do you think that will suffice?
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23rd January 2009, 08:20 AM #6
Hi Fossil...
I'd try to modify the slot so that it copies the curve of the inside edge of the knife. That way when you lower the knife you can maintain the same clearance to the saw blade.
I had to modify my Felder knife this way...I used a die grinder.
I'm told that European safety regulations prohibit trenching cuts where the blade is buried in the work piece, hence the riving knife sitting above the arc of the blade. I didn't want to be bothered with taking it on and off , hence my modification.
Good luck
Greg
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23rd January 2009, 09:45 AM #7.
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You should be able to drill this with either a tile drill bit or a masonry bit. Slow speed and lots of lube. For 8 mm you might need a 4 mm first pass.
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23rd January 2009, 09:49 AM #8I'd try to modify the slot so that it copies the curve of the inside edge of the knife. That way when you lower the knife you can maintain the same clearance to the saw blade.
I think that's what I'll do.
I'm told that European safety regulations prohibit trenching cuts where the blade is buried in the work piece, hence the riving knife sitting above the arc of the blade. I didn't want to be bothered with taking it on and off , hence my modification.
Anyway, thanks for the replies.... back to work now.
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26th October 2009, 12:31 PM #9GOLD MEMBER
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I know it is a little old but ---
How did it go?
Anyone else done it?
I have a MJ2325B from Carba-Tec and was wanting to groove a piece of timber with a 3mm groove but the riving knife is some 30mm too high to allow this. Normally I would use a router but the groove is too narrow - I'm not keen to remove the riving knife to do this but would like the knife to be just a fraction below top tooth height to extend my options.
Any thoughts?
Regards,
Bob
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26th October 2009, 01:27 PM #10Hi Fossil...
I'd try to modify the slot so that it copies the curve of the inside edge of the knife. That way when you lower the knife you can maintain the same clearance to the saw blade.
I had to modify my Felder knife this way...I used a die grinder.
I'm told that European safety regulations prohibit trenching cuts where the blade is buried in the work piece, hence the riving knife sitting above the arc of the blade. I didn't want to be bothered with taking it on and off , hence my modification.
Good luck
Greg
Doesn't look 100% but works perfectly.
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27th October 2009, 10:07 AM #11GOLD MEMBER
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Thanks for the reply.
I'll have a closer look at this option.
The other option I'm considering is to simply remove the 30mm from the top and make a replacement overhead clear guard and dust extraction - the current guard is red plastic with very marginal dust collection.
Regards,
Bob
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