Spindle Runout

scott216
Posts: 228
Joined: Thu Oct 10, 2013 12:35 pm
Location: New Jersey

Re: Spindle Runout

Post by scott216 » Sat May 03, 2014 7:02 pm

I'm trying to mill a PCB with my ShapeOko 2 and a dewalt DW660. On my first attempt it was clear I had some runout, so I took some measurements on the dewalt. Measuring the runout of the bit itself with it mounted in the DW660 I got about 4 mils. Then I checked the OD of the DW660 shaft, right above the threads where the shaft is smooth the runout was very small, less then 1/2 mil . Next I measured the ID down near the bottom and I got 1.2 mills. I measured the ID up into the shaft about 1/2 inch and I got about 3/4 mil runout. I'd say that's pretty decent. So what I'm trying figure out is which surfaces are critical for runout. The collar is not a tight fit on the shaft ID, so I'm thinking the two tapered ends of the collet and where they mate are the important surfaces. These would the step inside the shaft and the ID of the nut. Am I thinking about this correctly?
Shapeoko v2 with DW660
GRBL v0.9i
Location: New Jersey

Nigel K Tolley
Posts: 226
Joined: Sat Feb 08, 2014 4:06 pm

Re: Spindle Runout

Post by Nigel K Tolley » Sun May 04, 2014 10:55 am

The critical thing is that the toolbit doesn't vibrate or get too much force applied during the cut.

The lower run-out you have the finer the cutter you can use and the finer a line you can engrave.

Have a look at your setup and see what run-out you get with a ground steel rod in the chuck/collet. That is what helps the most because that is where it matters.

Note that a slight vertical misalignment will lead to bigger issues than a fractionally increased run-out.

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WillAdams
Posts: 8618
Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Spindle Runout

Post by WillAdams » Sun May 04, 2014 6:35 pm

Nigel K Tolley wrote:Note that a slight vertical misalignment will lead to bigger issues than a fractionally increased run-out.
Details for doing that on the wiki: http://www.shapeoko.com/wiki/index.php/ ... he_Spindle
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

TDA
Posts: 31
Joined: Wed Dec 18, 2013 11:14 pm

Re: Spindle Runout

Post by TDA » Tue May 13, 2014 6:01 pm

Sorry to respond to this so late. Been tied up with things.

Missed the reply to my question on the HF router. Unfortunately that is the same style collet we looked at before. Not a lot you can do with it with so little mating surface.

Anyway, to answer your questions Scott. 4 mils is a lot if you are trying to use trace isolation tools (V style). It will also limit your endmill choices. Typically you have about 10% of the diameter of the tool in runout before you run into big issues.

The critical surfaces for most collets is the taper angles. They have to have matching angles to the collet and bore while having low runout. If you have the wrong angle in either then the collet is typically pinched at one point. This leads to more runout as the collet can shift inside the bore. This will usually result in angular runout which is the worst kind as it gets worse the farther from the face of the collet you get. This isn't to say that there's not other places that you can get runout. In a spring style collet you can have a leaf that is thicker than the others. This will usually skew the tool to one side causing more runout. And if the bore of the router isn't concentric then this will also contribute. If you want more details let me know.

One last thing on measuring runout. If you are using a tool or rod to measure it make sure it spec'ed for it. A lot of tools and rod will have runout of their own. Most high end carbide is made from centerless ground shanks. These are usually pretty good to use.
John Torrez
Think & Tinker / PreciseBits

scott216
Posts: 228
Joined: Thu Oct 10, 2013 12:35 pm
Location: New Jersey

Re: Spindle Runout

Post by scott216 » Tue May 13, 2014 6:17 pm

TDA wrote: 4 mils is a lot if you are trying to use trace isolation tools (V style). It will also limit your endmill choices. Typically you have about 10% of the diameter of the tool in runout before you run into big issues. .
I've got a couple 0.3mm end mills that should arrive today. I'll see how they do compared to the v-bits. Even with these new bits, it's way above your 10% guideline.

One last thing on measuring runout. If you are using a tool or rod to measure it make sure it spec'ed for it. A lot of tools and rod will have runout of their own. Most high end carbide is made from centerless ground shanks. These are usually pretty good to use.
I was measuring the bit's shaft, near the collet I was thinking of getting a calibration shaft from PreciseBits. This will also help me see if I've got angular runout.
Shapeoko v2 with DW660
GRBL v0.9i
Location: New Jersey

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