Spindle Runout Problem

[w102acd]

All,

I have built a DIY CNC machine out of MDF with THK linear rails and ACME threaded rods and nuts. The limits of the machine are 30" x 20" x 10".

I have built a mount for the a Rotozip. Up until now I have only used the machine to make cute little engravings in MDF. It has worked well for that. I ordered the HobbyCNC kit with motors and installed them. I can now move much faster and smoother.

I then ordered some 1/4" diameter / 6" long carbide ball end mills. I was hoping to run some parts this morning, but ran into a huge snag. The runout on the end of the bit is anywhere from 0.060" to 0.120". YIKES!!!

The Rotozip I got is refurbished from Amazon. I realize my bit is very long and I will likely have some runout at the tip. My questions are:

Is this typical for a Rotozip to have this much runout???

Would getting a new collet set from Home Depot possibly fix the problem???

Would getting a new Rotozip fix the problem???

Should I upgrade to a laminate trimmer (like a Porter Cable or Hitachi)???

Budget is important and my machine is not too strong so I need to keep the spindle as light as possible. By the way, right now I am cutting all kinds of woods (oak, pine, mdf, etc). I would like to eventually cut aluminum. I can handle taking light cuts and taking a long time to get a part as this is not a production machine.

Thanks in advance,
Andy

[ger21]

A rotozip was not designed to be a router, or even to make precise cuts, so that doesn't sound unreasonable.

Why do you need a 6" bit? You should always use the shortest possible bit, as the longer they are, the less rigid they are, and the more they magnify your runout. And you'll always have some runout. A laminate trimmer will be better, but i still wouldn't recommend using a 6" bit in one. If you want the least amount of runout, your best bet is to get a Bosch Colt laminate trimmer and a precision collet from http://www.precisebits.com/products/...h_Colt_Collets

[CarveOne]

A slender 1/4" bit 6" long in a zero run-out router will still chatter like crazy as soon as it contacts the material to be cut due to flexing of the bit and your machine. I know that one in a 5 hp spindle in a 5x10 ShopBot router will do it on the molds that I use in my work.

Part of your problem could be the 10" Z travel, which is a lot of leverage if it is at the lowest or highest position.

CarveOne

[w102acd]

Gerry,

Thanks for the reply!

I just wanted to be able to take advantage of my 10" z-axis. This would allow me to reach all the way through a 5" piece if I wanted to.

The Bosch Colt with the collets seems like a reasonable combination. I really appreciate the advice. What would a reasonable runout be at the tip of a bit 5" from the collet nut???

Thanks again,
Andy

[ger21]

Originally Posted by w102acd What would a reasonable runout be at the tip of a bit 5" from the collet nut???

Zero. (I really don't know) Honestly, I'd stand back when turning that thing on, because if it has some runout, it might start shaking like crazy. Like I said, unless you are actually trying to cut something 5" thick, you should use a much shorter bit. As CarveOne said, long bits don't cut very well due to chatter, unless you take extremely light cuts.

[w102acd]

Thanks guys!!!

So basically even if I had this bit in a zero runout situation, I could not really cut anything with it??? This is regardless of the machine I have it in???

I was looking around and noticed that people either like the Bosch Colt or the Porter Cable 7310. The Colt I saw was 1 HP and the 7310 I saw was 3 HP. The 7310 is cheaper and there appear to be good reviews on it's runout with stock collets. What do you guys think???

I will probably just use some shorter bits for the time being to test out my new motors. Then when I need the accuracy I can get a different spindle.

Thanks again,
Andy

[ger21]

If you get a Colt, be sure to get the variable speed. Th fixed speed version spins too fast.

The 7310 is not 3 HP. It has less power than the Colt. I have a 7310, and we have a few Colts at work. The Colt is a bit bigger, and heavier, but probably easier to mount due to it's round body. Since the price is so similar, I'd go with the Colt and get the good collets for it.

[w102acd]

I have another question:
Is there a lower speed spindle option??? I would be interested in speeds more like a traditional CNC machine has (~4000 RPMs).

I find it hard to believe that no one has a lower speed spindle option for a DIY CNC machine.

Everyone seems to want higher speeds (router/ultrasonic spindle). What is the benefit of this??? Remove material faster???

Chances are at router speeds my machine would never be able to travel fast enough.

At first glance, it should not be that difficult to make a low speed spindle. Thoughts???

Thanks,
Andy

[FandZ]

Originally Posted by w102acd I have another question: Is there a lower speed spindle option??? I would be interested in speeds more like a traditional CNC machine has (~4000 RPMs). I find it hard to believe that no one has a lower speed spindle option for a DIY CNC machine. Everyone seems to want higher speeds (router/ultrasonic spindle).

I think we all would love a low speed sutup, but they tend to be pricey. You'd have to look into getting a spindle withe a VFD setup. The Chinese ebay ones tend to be the cheapest option. Then there are other custom options, which involves gears and belts to reduce the speed of the spindle, like how a drill press works. I'm still gaining experience but I haven't seen any problems with a slow feed rate and a good bit. I've done tests on MDF, HDPE, and various woods. I know some people have mentioned smoking if they go too slow but I haven't seen it. I'm wondering if they are useing too low of a spindle speed and too deep of a cut.

I'm useing a Hitachi router.

[jsheerin]

http://www.cnczone.com/forums/showthread.php?t=32609
Check out this thread. He uses the head off a Chinese mill as a spindle. This might have problems going fast enough, but you would definitely get the lower speed range.