Centering router's bit when router is in a lift?

  • Advertise with us

« back to Power Tools, Hardware and Accessories forum

Forum topic by LD100 posted 01-05-2021 05:58 AM 1221 views 1 time favorited 20 replies Add to Favorites Watch
View LD100's profile


9 posts in 170 days

01-05-2021 05:58 AM

Topic tags/keywords: lift table centering bit

I am looking for relevant advice for those experienced with router lifts.

I purchased a new router table and router lift. The lift came with one phenolic insert. I do intend to purchase an expanded set of inserts, but for now I just have the one.

I installed my older Porter Cable 690 router into the lift and immediately noticed that the collet appeared a bit off center when looking down at the phenolic insert from above. I knew this could be that the outer hex on the collet could be off center, and I knew that it is only the bit’s position in the collet that really matters.

To confirm and quantify things, I took a small rectangle of waferboard and drilled a 1/4 inch hole in it plus a tiny hole a distance away for a pencil tip. I put that same drill bit into the collet, slid the waferboard down onto the bit, and used it as a “compass” to scribe a circle onto the phenolic insert. This allowed me to confirm any offset from dead center, and also quantify it to some degree using my digital calipers. I could plainly see that the pencil lead circle was not concentric with the insert.

I discovered that with the Porter-Cable 690 my collet is off center by at least 0.010-0.012 inch. As a sanity check, I removed the Porter-Cable router and installed my new Bosch router and repeated the scribing and measurement. I discovered the offset was worse, about 0.039”.

When using bushings with routers, we all know the importance of having the bushing centered on the bit, and there are many guides and videos describing how to center a router base plate on a HAND HELD router using a centering cone, etc. In my case, the router is clamped in a router table lift, and so I am wondering how is it that routers in lifts are typically centered to the insert above them. I do plan on leaving my Porter-Cable router permanently in the lift, so I’d like to center it as perfectly as I can and leave it alone.

Here are my questions:

(1) Is a router’s XY position typically adjustable with respect to the lift? (not talking about the up/down lift position here). Are they generally aligned at the factory and that’s it forever? I am hoping to hear that your router lifts all have a way to adjust and lock down the axis position for a given router, and that I need only learn how to do that on my lift.

My internet research has found that some people have never ever adjusted their lifts and have never had any issues, and if this is true for you that is great, but hearing of such cases doesn’t address my question.

(2) It might be said that nothing in woodworking is perfect, only “perfect enough.” There is a tolerance between a router’s outer diameter (OD) and the bit’s axis, and tolerances from the router clamp on up though the lift mechanism and to the phenolic insert above. Therefore it might be argued that the alignment of a router bit axis and a bushing screwed into a phenolic insert will never be absolute perfection. My question is what is the max acceptable offset such that template work still turns out decently? I’ve seen dovetail joints that are not centered due to bushing-bit misalignment and I would like to minimize this issue as much as I can.

I would expect many people will not have considered this question before, but if you have, I’d like to hear what you think. How much misalignment can there be before template work quality begins to suffer?

Thank you for your thoughts.


20 replies so far

View Andybb's profile


3248 posts in 1658 days

#1 posted 01-05-2021 08:26 AM


Unless it is drastically off-center I wouldn’t give it a second thought. Just make sure you use an insert wide enough for the bit you’re using. Even 3/100 of an inch seems inconsequential.

-- Andy - Seattle USA

View Rich's profile (online now)


6779 posts in 1644 days

#2 posted 01-05-2021 12:49 PM

Andy is right. It doesn’t matter.

However, without knowing what lift you have it’s impossible to advise you on moving the motor in the lift to get it centered.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View HokieKen's profile (online now)


17301 posts in 2193 days

#3 posted 01-05-2021 01:27 PM

The only time it would matter is if you have a throat insert that accepts template bushings and are using those bushings.

If that’s the case, you probably need to be able to tweek your position. But, like Rich said, we can’t really offer advice without more details.

-- I collect hobbies. There is no sense in limiting yourself (Don W) - - - - - - - - Kenny in SW VA

View jbmaine's profile


159 posts in 525 days

#4 posted 01-05-2021 01:38 PM

I’ve had a lift for years and never gave centering the bit a thought. Then I bought a Leigh RTJ400 and found my router was out of center to the lift and had all kinds of problems trying to use the elliptic bushing. I ended up shimming the router to bring it back into concentricity. I’m a retired tool and die maker and have lots of measuring tools so this is how I checked it.

At the end of the day, unless you try to use bushings, concentricity should not matter.

View northwoodsman's profile


526 posts in 4801 days

#5 posted 01-05-2021 02:02 PM

Templates used in a router table application are most often referenced off a bearing on the bit so the placement of the router in opening shouldn’t matter. I have 9 routers and you got me thinking… I don’t ever recall using a bushing set-up in my router table, nor can I think of an instance where I would. If it keeps you up at night you could always use shims to center your router in the lift. Is there any room to rotate your router in the lift? Perhaps that’s all it would take.

-- NorthWoodsMan

View splintergroup's profile


4978 posts in 2277 days

#6 posted 01-05-2021 02:48 PM

A year ago I revisited the router installation in my older Woodpecker PRL (looks almost exactly like jblmaine’s picture above).

I noticed that the router was not quite perfectly square to the surface so I spent some time setting it up square with the collar that secures the motor to the lift. These lifts are CNC machined and should be plenty well machined with their mechanism perfectly centered and square to the top plate. Any misalignment most probably is caused by the router not being installed correctly.

What I did different to correct my problem was to tighten the collar to my router motor until I could still just spin the motor in the collar by hand. I felt a small “thunk” and the motor loosened up a bit. I had tightened the collar while the motor was slightly cocked and the proceedure allowed it to pop into alignment. After snugging up the collar again, everything stayed true.

jb shows am excellent way to precisely measure for centering and if you let the indicator ride on the surface, it also will show you if it is all perpendicular to the surface.

If after being sure your router shaft is truly perpendicular to the table surface and these type of steps don’t fully correct any X/Y offset, you’ll need to try shimming between the motor and collar. Your 0.012” is not much and even a section of aluminum can or a few layers of paper can work in a pinch.

Also don’t be afraid to rotate the motor in the collar and try different positions. Any off center in the router motor machining can be used to compensate for any off center machining/assembly in the lift

View GR8HUNTER's profile


8337 posts in 1767 days

#7 posted 01-05-2021 03:34 PM

DO THIS :<)))))))))))

-- Tony---- Reinholds,Pa.------ REMEMBER TO ALWAYS HAVE FUN :<))

View LD100's profile


9 posts in 170 days

#8 posted 01-05-2021 04:45 PM

Hello all. First, I want to express my thanks for all of your thoughtful responses.

I agree with much of what has been said. It doesn’t matter if the bit is offset from the insert in a router table unless bushings are involved. Bushings don’t directly attach to bits like bearings do, so in this case bit to insert coaxial alignment is important. (Hence the use of centering cones on hand held routers.)

The Leigh RTJ400 is exactly the jig I had in mind that triggered this thread. This particular jig is for router tables only, and you move the jig (and the work piece), not the router. The guide bushing is attached to the table insert and it is elliptical. Because it’s elliptical, by rotating it judiciously one can actually tune the fit of the joint (loose vs tight). However, if the bit isn’t centered on the insert, the jig won’t work as expected. All your tails will be shifted. Which direction and how much they are shifted depends on the offset error in your particular router table.

For those interested here is an old video discussing this jig. (in the video, it’s mentioned that the jig includes a DVD! What’s that?)

When installing my Porter Cable router into my table, I observed that when I rotated the router body, or even simply removed it and put it back in, a slightly different offset error would result. I found this a bit maddening because it was seemingly random. Your tips and comments are all helpful here and dead on.

If I can get my router centered to my satisfaction and lock it in place, I will be happy leaving the Porter Cable permanently in place and call it good.

I purposely did not mention my particular equipment because I was looking for general information. I did not want to start a discussion about “this brand vs that brand” since my purchase is a done deal for now. My lift is a SawStop lift, and I chose this lift because I like the design of the lift mechanism and it’s preconfigured for my saw. The clamp mechanism on it is simple, which I like, but the alignment between this clamp mechanism and the table seems entirely dependent upon SawStop’s component accuracy or perhaps a factory alignment step. There is no mention of a way to adjust the clamp position. I have reached out to SawStop to inquire but no answer yet.

The router clamp has a 4.2 inch diameter. It is aluminum and is held in position by three fasteners (see arrows). I don’t know if the fasteners are locating (e.g. precision shoulder screws) or if the clamp is simply jig-located in the factory and the fasteners locked down.

SawStop includes collars for 3.25 inch and 3.50 inch diameter routers. The manual is vague in my opinion, saying that “if your router is significantly smaller, use a collar.” The clamp is not designed for routers larger than 4.2 inches, and the manual fails to mention that if your router isn’t exactly either 3.25” or 3.50” their included collars are not going to work. The aluminum clamp flexes when tightened but it is not designed to flex much. With the provided sizes they are covering “most routers” out in the world, although I have read complaints about router compatibility with this lift and SawStop’s failure to make this crystal clear up front to shoppers.

One thought I had was that I could loosen the three bolts, reposition the clamp, and re-tighten. I would not do this without express guidance from SawStop. (I don’t want to lose a factory alignment and then create a nightmare for myself.)

My background is mechanical engineering and I regularly work closely with tool and die makers. Thanks again for all of your advice.

View Andybb's profile


3248 posts in 1658 days

#9 posted 01-05-2021 04:52 PM

DO THIS :<)))))))))))



-- Andy - Seattle USA

View splintergroup's profile


4978 posts in 2277 days

#10 posted 01-05-2021 05:22 PM

Another simple technique that I used before resorting to the dial gauges is to select a guide bushing with either a 1/2” ID (best) or a 1/4” ID if you don’t have a 1/2”.

Hopefully the bushing has a good fit into your insert for a permanent fix, but some slop can be useful.

Assuming you have your router mounted as vertical as possible, chuck up a 1/2” drill bit or other precision 1/2” rod.

With the bushing installed, you should be able to “coax” the router enough to allow the shaft to slip in/out of the bushing as it is raised/lowered.

If your bushing has some slop in the insert, you can raise the router and slide the bushing retaining nut over the shaft and let it slide down to the router. With the shaft raised above the table surface, slide the bushing over the shaft and into the insert.

If you have enough hand room underneath, you might be able to spin the nut onto the bushing and snug it up a bit, effectively centering it. Lower the router so the shaft is out of the bushing, carefully remove the insert and tighten up the bushing.

Reinstall the insert/bushing with the same indexing and you should be near dead centered.
This worked well for me, but with a different lift there may be issues that make it un-doable 8^)

View LD100's profile


9 posts in 170 days

#11 posted 01-05-2021 05:28 PM

Thanks, splintergroup. That is exactly the process I had in mind with a variation. I was going to use a Jessum insert with a 1/2” opening.

The insert can be seen here.

View HokieKen's profile (online now)


17301 posts in 2193 days

#12 posted 01-05-2021 05:30 PM

If I’m understanding the clamping mechanism correctly, any deviation from the nominal diameter of 4.2” will shift the router off-center by 1/2 that amount. This is based on one side of the clamp being fixed and the other side moving when clamping. So if your router measures 4.15” diameter instead of 4.2”, you’re spindle will be off-center by .025”.

If that is the case, I don’t really see any option other than to adjust the position of the clamp for the router being used. I’ll be curious what SS has to say about it. As far as loosing the factory alignment… it doesn’t sound to me like you can make it any worse.

-- I collect hobbies. There is no sense in limiting yourself (Don W) - - - - - - - - Kenny in SW VA

View LD100's profile


9 posts in 170 days

#13 posted 01-05-2021 06:22 PM

HokieKen, you are exactly right.

The two supplied plastic router collars (3.25” & 3.50” ID) have a 4.2” OD. However these collars are split collars which allows them to snug down on your particular router. Therefore the OD of the collar can deviate a bit depending on your exact router OD.

Looking at the clamp, the “theoretical center” of the clamp is fixed in place with some location tolerance (whatever it is). In addition, if your collar+router OD is not exactly 4.20” your router center will shift off center, adding to any offset error. The clamp is clean and simple, but has issues. It is what it is, I guess. I haven’t explored JessEm’s lift in detail, but the JessEm clamp seems to have 4 clamp elements coming in from four corners. This would suggest it’s more accurate for centering than SawStop’s clamp, but maybe it isn’t in actual practice. Not sure.

So far, I love the SawStop’s lift mechanism but I don’t love its clamping mechanism. I don’t hate it, but I just don’t think it’s that great. I’m suspending final judgement while hoping I will get mine centered good enough in the end and leave it in place.

I will definitely post anything I hear from SawStop.

View HokieKen's profile (online now)


17301 posts in 2193 days

#14 posted 01-05-2021 07:41 PM

If your router diameter (or collar diameter when clamped on the router) are smaller than 4.2”, you could use shim stock to get the router centered. If your router/collar are larger than 4.2”, that won’t work though. That of course assumes that the clamp is perfectly centered to the insert at the nominal 4.2”.

-- I collect hobbies. There is no sense in limiting yourself (Don W) - - - - - - - - Kenny in SW VA

View LD100's profile


9 posts in 170 days

#15 posted 01-10-2021 02:15 AM

Last week has fully passed and I haven’t yet heard back from SawStop. Oh well.

I purchased a set of phenolic inserts from Lee Valley. They work with the SawStop router table. I used a 1/2 inch drill bit (which is 0.495 inch by my calipers) in my router’s collet and used the 1/2 inch phenolic insert (hole diameter was about 0.510 inch and not perfectly circular) as a guide, with the goal of my drill bit turning by hand without scraping the guide.

It took about 1.25 hours. Through both the careful application of painters tape to the body of my router, and rotating my router in the lift’s clamp, I was finally able to find the sweet spot where the bit turned freely in the insert. And, I could look down on the bit from above and see a small consistent gap between the bit and the hole. Based on the above I am probably with 0.005 inch of center.

I plan on leaving this router in place on the lift and see how it goes. Hopefully I won’t have to revisit it for a good while. Thanks for your tips.


showing 1 through 15 of 20 replies

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics