PC Router / collet / bit questions

[jsheerin]

I broke a bit tonight and am wondering about a few things so I can try to prevent this in the future. I was cutting MDF at 50ipm, ~16k rpm, 0.25" DOC with a 0.25" diameter 2 flute straight router bit with carbide blades. The bit was extending out of the collet about 1.25". The bit broke at the bottom of the collet. When I took it apart, there was a bit of rust on the bit's shank there. So to me, that's a text book fracture - rust spot causes a stress riser and it breaks there. I'm wondering how to prevent this in the future, as the cutting edges looked fine still.

So do you guys put any kind of lube on your bits or in your collets? I've been reading precisebits.com about taking care of spindle bores, and I've read about cleaning out collets on another website, but neither of them specifically address this.

Sort of related to this, my router is a PC892. It gets very hot when running for any length of time. The heat seems to come from the spindle bearing area. The collet and bit are always really hot. This happens even if I just run the router in air, not cutting anything, so I think it's an issue with the router, not me creating excess heat from cutting too slowly or something like that. I'm not blocking the router's air flow. So I'm just wondering if this is normal for these routers.

Thanks,
John

[stevespo]

Was it a solid carbide bit, or a steel shank with carbide brazed onto it? Your feedrate and DOC seem reasonable, but I'd run that at full speed (24K RPM) next time. I know it's noisier, but you'll get better results running it faster, and less load on the tool.

If I notice any light surface rust, I use steel wool and WD-40 to clean them up. A light coat of WD-40 seems to help keep the rust at bay during the summer months. I wouldn't think that mild rust or even pitting would be enough to cause a stress-riser type failure, but I really couldn't say.

I do have a couple of PC892 series routers. The first two ran very cool. When I bought the third one, it ran hot right out of the box. I contacted tech support and they told me that they had recently changed the bearings and that the router would run hot until it was broken in. It seemed odd to me, but sure enough, it's running very cool now. I would estimate this was after 50-100 hours of use, but I wasn't keeping track.

Steve

[jsheerin]

Hi Steve,
Thanks for the info.

It was a steel shank with brazed on carbide blades.

You got me - I am running slower to lower the noise a bit. My router's in my detached garage, and the noise is not attenuated very much. My neighbors are just as close to my garage as me, so I'm trying to avoid annoying them too much. Maybe I should start working on an active noise reduction system for it...

Thanks,
John

[stevespo]

John, you're fine running the bit at 16K RPM, but I would probably decrease the depth of cut. Short of building an enclosure or installing a 3 phase spindle, noise is going to be an issue. Those PC routers do get noisy above 16K, but are pretty quiet below that.

For DOC, I generally use 1/2 of the diameter of the bit, but I'm pretty conservative about this. Lots of people run much more aggressively, but my preference is for light cuts and faster feedrates. Personally, I'd probably run 90-100 IPM, 24K RPM and .125 DOC, but there are lots of ways to make it work.

Also consider a 1/4" solid carbide up cut bit for general woodworking.

Steve

[jsheerin]

Thanks Steve,
I'll play around with my speeds and feeds some more.

Actually I was trying to find a solid carbide upcut at MSC the other day when they were having a sale. The straight bits don't evacuate sawdust at all, so I end up having to pick a lot of it out of my cuts by hand. I have a dust shoe, so I'd rather it just get sucked up. Anyway, I found several recommended bits on Onsrud's website, but I couldn't find them at MSC, so I didn't get any. Does anyone have any recommendations for MDF? I don't really want to drop $20-$30 if I'm not getting something that specifically for what I'm cutting....

Thanks,
John

[stevespo]

I don't have any specific recommendations for MDF. Maybe someone else will jump in here?

I have quite a few "general purpose" (upcut and downcut) spiral bits that I use in MDF, solid wood, some plastics, etc. I've used Onsrud, Whiteside, even some "lower cost" bits (from Grizzly, Rockler, Woodcraft) with very good results.

You may also want to consider a spiral downcut for pocketing and profiling in MDF. This will leave a very clean top surface with no chipping or fuzziness. The downside is that they are not great for plunging (ramping helps) and it doesn't not evacuate the dust as effectively.

Carbide endmills for metalworking will do the job, but the geometry and cutting edges are a bit different on the bits designed specifically for wood. There is an amazing variety of specialized tooling out there and it's difficult to sort things out. Perhaps start with one 1/4" upcut and one downcut and take it from there.

Steve

[ger21]

MDF is really hard on bits, so try to find cheaper ones. I've never used them, but you might want to try these.
http://www.mlcswoodworking.com/shops.../bt_solid.html

The reason your bit broke is because of the collet putting pressure there. Carbide won't break like that, but you may want to get a new collet just in case.

[jsheerin]

Thanks guys. I got some Whiteside bits from woodworkersworld.net - an upcut and a downcut to try.

I've started spraying out my collet with WD 40 every time I change bits to try to clean it out. Despite that, it marked up my new bit (steel shank, same as before) the first time I used it. This is just the standard PC collet. It almost looks like the bit is slipping in the collet, but the marks don't go around - they're just in spots. I will try to take a picture and post it - it's strange.

I've also changed my DOC and feedrate. Currently I'm just trying that - I haven't swapped the new bits in yet.

[ger21]

If the collet leaves marks, then get a new collet. Although some of my PC collets leave marks as well, but they've never caused a broken bit. But, I also rarely use 1/4" shank bits. As I said, the collet won't leave marks on the carbide bits. You might also try the Precise Bits collets. A bit more money, but very high quality.

[jsheerin]

I was looking at the Precise Bits collets originally, but I think once I wear this router out I'll be switching to one of the Chinese spindles so I'm not sure I want to spend the money. I've got a pile of VFD's sitting around I can use for controlling a spindle, so it seems like a good way to go. I was also planning on going to 1/2" bits for some production work I'm going to start doing. I'm using the 1/4" ones right now because I nested my current project really closely together and it has some small details that I needed the smaller bit for. I suppose if the collet is actually causing the break, I could go with a 1/2" shank bit with a 1/4" cutting diameter...

Thanks,
John

[ger21]

Like I said, then just use solid carbide bits. They won't break from the collet.

[pminmo]

Reminds me of a scary episode I had some 30 years ago. Had a router inverted in a table using a 1/4" straight bit. As I was cutting it broke and I heard the bit fly just past my ear! After composing myself and checking my underwear, I examined the bit. At the place where the bit broke was an obvious hairline rust spot that wasn't visable when it was intact. The event brought a whole new meaning to shop safety to me.