Router trouble

[ben vollmer]

Hello...
I've got a porter cable 890. It's maybe 15 years old but little used, and I'm pretty new to it.

Despite that, I'm taking on a big workbench build and trying to route out the square dog holes in the top in one of the board before laminating it into the top. (like https://www.youtube.com/watch?v=_xrIXr5Shno).

I hogged out most of the waste with a circ saw and chisel first, and then started routing to a template with a 1/2" x 1" bit like these: ( https://www.leevalley.com/en-us/shop/tools/power-tool-accessories/router-bits/30166-template-bits ).

I was trying to be take pretty conservative cuts as I worked down toward a final depth of 1", but I found a couple of times that the cut depth slipped deeper on me mid pass, I think mostly when I'd get to the far side of the cut and the bit would come out of the cut before I changed directions and brought the router back toward me. I also had the bit go up once, causing the bearing to go above my template and the bit to take a chunk of the workpiece and the template.

In each case my eyes were too laser focused on my path to really understand the mechanism of what was happening. I'm not sure if the bit was slipping in the collet, which I thought was pretty tight, or if the router is slipping in the base.

I don't think I had the bit bottomed out in the collet, which I understand to be bad technique... Is there something else I could be doing wrong technique-wise? Should I chuck the fixed base and just use the plunge one going forward? or a collet issue?
Thanks!

[Thomas McCurnin]

Not sure what is going on either. I would run some test cuts on scrap and see if you can tell what is going wrong. I don't bottom out the router bit, but it is just shy (1/16) of doing so. With those flush trim bits, I don't think I would want to take much more than a 16th off, especially if the stock is over an inch. Taking too much off will stress the router. I don't think the base has anything to do with this problem. Again, I'd look at tightening the bit, not taking off too much stock. Again, I'd run some test cuts to see if you can replicate the problem and address it.

[Marc Fenneuff]

The 890 plunge base has its strengths and its weaknesses. The cam lock lever does slip on me from time to time. But I can’t say that I’ve had the depth adjuster slip. I have learned to not rely on the collet lock when tightening bits - it's better to use two wrenches. I tore up a guide bushing the last time I only used the collet lock while tightening the bit, and the bit loosened up.

[andy bessette]

If the bit is slipping inside the collet, even though you've tightened it with sufficient force, then replace the collet.

[Jim Becker]

Two possible causes for the change in height:

1) bit slipping in the collet. If so, replace the collet...they do go bad
2) depth adjustment lock on the router is slipping. Troubleshoot accordingly

[ben vollmer]

OK, thanks everyone. I'm thinking I'll inspect the collet and reinstall and run some test cuts, replace it if it doesn't seem trust worthy.

[Brian Tymchak]

If the bit is slipping in the collet, there should most likely be some scratch marks on the shank of the bit. If the shank is clean I would look elsewhere for the issue.

[Jim Dwight]

If your bit has a 1/4 shank you may want to switch to a 1/2 inch shank bit. You cannot "lean on" a bit with a 1/4 shank nearly as much as you can a 1/2 inch shank bit. I only use 1/4 inch shanks for little bits I may also want to use in my Bosch colt (which only takes 1/4 inch shanks). Your PC 890 should have both types of collets.

Your collet could be damaged but I have found PC collets to work very well. I have two PC 690s and a big 7528 in my router table. Even the big one uses the same collets. But even my 690s have a lot more power than I feel comfortable putting on a 1/4 inch shank bit.

What you describe should be easily within the capability of your router.

[Richard Coers]

It would not be an easy job to "inspect" the collet. You will need quality measuring tools and a way to verify the bore of the collet is the same diameter over the full length. In my experience and study, I've accepted the idea that the internal bore develops a bit of an hour glass shape to the loads placed on it by the bit. Once that starts I think it rapidly accelerates. Collets are cheap, buying a new one and it should be a quick fix. But as mentioned, if you are doing a 1" deep cut with a 1/4" shank router bit, there is your real problem! Vibration.

[andy bessette]

RC--good post.