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Feed Speed
Table saw feed rate indicator based on cutter tip temp | |
My husband is a woodworker and has a "Northfield" table saw that he loves more than me. I sometimes go out into his shop and watch him work. When he is working with particularly dense or fragile hardwoods he has to be careful about how fast he feeds the stock through the saw. Too fast and the cut can
be ragged, too slow and it can scorch or burn (especially if with both dense and naturally oily woods like cocobola). This evening he mentioned that most mistakes are made when people feed the wood too slowly; too gingerly.
His comment made me think about how an interactive feed rate indicator might be designed.
My thought: a thermal imager mounted below the feed surface that reads the cutter tip temperature of the whirling blade and drives a segmented LED (or other) display up on top of the saw. If the feed rate is too low the cutter temp will rise and the imager will send a signal to the display which, in turn, tells the operator to increase the feed rate.
I don't have a solution for too high a feed rate, though.
Northfield table saw
http://www.northfie.../tablesaws/4saw.htm
Except his has a bigger table than this one. [bristolz, Oct 20 2002]
[link]
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Good idea, anything which helps a craftsman to do a better job can't be a bad thing. About too fast or slow a feed rate; what if the thermal imager directly controlled the R.P.M,s of the blade, to keep the optimum heat level regardless of how fast or slow the wood was being fed in. For someone who is a professional, having to take your eyes away from what you are concentrating on to glance at a display may result in more inconsistancies than it would cure.
I don't know woodworking, but working daily with porceline, limestone, slate, and marble, has taught me that even small distractions can cause you to easily blow a cut. |
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How about an audible alert? The woodworker is probably already using his ears to detect the high feed rate, which slows the saw blade too much...
Something like the old fashioned cream separators. "clank clank" is too slow, "dingdingding" is too fast. |
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As my elf is a former custom cabinetmaker , I award you the coveted 7200 rpm croissant |
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Cocobola! I love the sound of it. |
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I’ve also burned wood in my ever-present incompetence during the occasionally building of wood prototypes. So, instead of a complicated and expensive thermal imager, which would be more expensive than the woodworking equipment that it was attached to, how about just running a filtered tube to the woodworker’s nose. (You can experiment on your husband.) That way he would detect the burning, and would know, within a few seconds anyway, if his feed rate was too slow. (And maybe a green smell if the rate was too fast.) |
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Perhaps a finer kerf blade will reduce some of the burning problems? |
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Ripping too fast is usually done by novices who think they've learned what to do. It also results in tearing on the back (top) of the cut. |
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I used to watch the effect on a test piece, before running a critical cut through a good piece of timber. Though I used mostly softwoods, as Oz hardwoods tend to be almost as hard as tungsten carbide and have a very dense, wavy grain. |
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To make life easier I use only Hitachi C-9 saws, whether handheld or set in the bench, or in the compound, sliding, mitre saw cradle. Same characteristics each time. |
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"...would be more expensive than the woodworking equipment that it was attached to..." |
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I think an inexpensive CCD imager in a rugged case could do this. I doubt it would be very expensive. Probably under $100. On the other hand, I think a good table saw is pretty expensive. At least they look expensive to me. |
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On the whole though, I admit this idea is not too well cut. |
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Depending upon the table, they sure are expensive. I paid over $1,000 for the table I have, without the saw. My saws were $340 each. |
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I don't have a particularly good table, but it does take routers and finishers... for a price. |
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The CCD idea is good. Alternately, you could have a computerised belt driven feed, set to alter speed for timber type, age and approximate moisture content. |
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Bris - you could buy very expensive woodworking equipment and a cheap camera, or you could skimp on the woodworking equipment and spend a bundle on the camera. I prefer to do the latter, because then what I said previously seems less stupid. |
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This is a good idea; but why does it need a feedback? What Bubya said in his last sentence. Twin 4" conveyor belts either side of the blade. |
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What about some type of "feeler" on one of the teeth on the saw blade? It could be a simple pressure sensor or something. When the wood was being fed too fast, the pressure would go up, and when the wood was being fed too slow, the pressure would go down. For the drive, I would use a chain with a "pusher" thingy at the end, which I beleive would be less likely to slip than a belt. |
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You don't need CCDs- why do you need to image? Just use an infrared photodiode, an opamp, and an LED or a buzzer. Pennies. |
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You're right. No imaging required. |
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The idea of a feeler will be subject to the incredibly variable pressure, due to feedstock density, on an individual tooth. Better to measure the increase/decrease in torque against the motor and adjust accordingly, I think. |
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I churned one up for [bris]. + |
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