Machsupport Forum
Tangent Corner => Tangent Corner => Topic started by: adprinter on September 01, 2009, 05:18:32 PM
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Hi all,
I have a Porter Cable LN690 router that I am using on my CNC build. I ran across a 7 to 1 ratio timing gear and belt set which I gleaned from some old equipment I have lying around my shop. The thought came to me, to mount the large timing gear in the router chuck, and install a second chuck to be driven by the smaller gear. With a 7 to 1 ratio, using the PC Router (27000 RPM no-load speed), that works out to an incredible 189000 RPM! My question to the group, has anyone ever done something like this? If so, what are your thoughts on designing a shaft and bearing assembly which could withstand such speeds? I realize that it will probably be much lower speeds than the math suggests, (especially once the cutter makes contact with the material being cut), and that quite possibly there are no bearings available which could support such speeds. I just wanted to know if anyone else has ever tried something like this?
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Hi, I would forget about it, no bearing could spin at that speed.
If it not balanced, something will break and it could be very dangerous.
As soon as you'll put power, the belt will snap.
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If you do decide to do it, take a video and you-tube it. It should be an interesting piece. The TV show "when disasters strike" comes to mind. :) I have thought about doing the same thing, but opposite of what your shooting for. A slower speed would be more feasible. In the end, after all the design, materials, and everything else to make a good solid unit, it would prolly be a better idea to just purchase a spindle designed for your needs.
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Before it gets to full speed, you'll be diving on the floor due to the noise it'll make. Then you'll hear a big bang.
Probably shouldn't attempt it. :)
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Thanks for everyone's input. After further research (for the bearings) I have dismissed the idea. At least with the 7 to 1 ratio. I may yet try a larger timing gear to drive the spindle. Something more along the lines of 2 to 1 ratio may actually be do-able. Lack of funds prevents me from buying a water-cooled VFD spindle motor to achieve the higher speeds, so it's the inventor in me that poses these questions. I have also designed an improved linear rail system, using swing bolts, small bearings, and square tube steel (as the rails). I will post the modified MyCNC.PDF once I complete the file for viewing -probably sometime tomorrow. It will (hopefully) provide for enough stability for machining aluminum. Again, thanks for the input!
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I am running an NSK spindle at 50 k but it has ceramic air cooled bearings. Just some food for though.
John