SOLVED: LR32 Hole position discrepancy of 0.5mm

[cliffp]

I am finding that I am getting a difference of 0.5mm in the position of my holes depending on whether I am using the right hand side of the guide rail or the left hand side. I have pretty much eliminated the possibility that the error could be due to a difference in the hole positions in the guide rail (very unlikely anyway as they are CNC machined) and I have used a digital caliper to measure the dimensions of the longitudinal stops and they seem to match to better than 0.1mm. I have also carefully checked the mounting of the router in the mounting plate and the tightness of the rubber strips against the guide rail. I have spoken to Festool UK and they have only suggested checking the things I have mentioned above. My conclusion is that the error is in the router mounting plate. Am I being unrealistic to expect better accuracy than this? The Festool representative seemed to think this error was larger than normal.

Any suggestions on any further tests to carry out?

 

[MahalaHomecraft]

I don't see how the problem could be in the plate... For an example, if you're drilling holes with 32mm oc spacing, by the time you get to the end of your rail you have 32.5mm between holes?  Or your holes run to 5mm off square?

 

[cliffp]

The spacing between the holes is 32mm. The problem is that each hole in a row of holes created using the right hand side of the rail is 0.5mm further from the reference edge (the one the longitudinal stop goes up against) than a row of holes created using the left hand side of the rail. In other words, whereas I would expect the hole positions to be 16, 48, 80, 112 etc, they are 16.5, 48.5, 80.5 and 112.5 from the edge. I am surprised because there doesn't seem to be any play in anything, the mandrel fits perfectly in the guide plate hole, the guide plate can't be rotated (ie the rubber strips have been adjusted properly) and there isn't even any discernible play in the location of the retractable pin in the guide rail holes. Everything is also clamped down tightly.

 

[otis04]

Is your work piece exactly at the right dimension and did you reference off the same edge of the workpiece?

 

[Sparktrician]

I'd have to ask, when you set things up, did you use the centering mandrel to align the router properly with the mounting plate?  If not, this can contribute to the inaccuracy experienced. 

 

[tiralie]

While I like using this system, the design of the stops can create small offsets between sides. Because the point at which the stop meets the side of the board is curved, any pressure can indent the side of panel you are putting the 32 mm holes into and thereby cause an offset.
In addition, if there are any imperfections in the cut, less or greater than 90 degrees, splinters etc. where the stop is resting it will create a small offset.
Check the space between the stop post and the threaded hole on both stops. Yours may be off slightly or there may be some discrepancy between the two as there is a little play in this area before it is tightened.
Tim

 

[MahalaHomecraft]

I just typed a lengthy reply , and as soon as  I was done I immediately understood what you were saying in your last post.  

Let's say you're standing at your work bench with your guide rail parallel to your stomach and the rubber edge facing away from you.
sit your LR32 on the rail in front of you.  With the pin in one of the holes on the rail, draw a mental line square off the rail connecting the pin to the large hole in which you're centering mandrel fits

Let's say that the true center of the hole is a quarter of a millimeter to the right of your mental line.

Then you would have 32.25 mm measuring off the left, and 31.75 mm measuring from the right.

Now if your tape measure is reading long by a quarter of a millimeter, you would be reading 32 mm off the left side and 32.5 mm off the right side.

Plausible?

 

[Michael Kellough]

Since the end stop is fixed to the hole in the rail the problem can't be with the rail itself. You could saw one end of the rail off and it wouldn't make any difference to the relationship of the end stop and the series of holes.

The likely problem is the position of the router in the base as Sparktrician said. If the router is off-center in the guide by 1/4 mm then you'll get a total difference of 1/2 mm if the system is used as designed.

If the router is installed correctly then the problem is the result of how the retractable pin fits the holes in the rail. There is discernible slack in my kit. To get perfectly placed holes that slack has to be taken up in the same direction no matter which side of the panel the guide is on.

Drilling holes in a cabinet side panel push the router/pin to the cabinet top side of the oval hole in the guide rail for both right and left sides of the panel. If you always work from the same end of the guide rail even when it is turned around on the panel you'll find a little difference in the distance of the holes to the end of the panel.

 

[cliffp]

Many thanks for all of the replies.

Is your work piece exactly at the right dimension and did you reference off the same edge of the workpiece?

Yes, I am aware that the workpiece needs to be exactly square to avoid errors in the hole positions. Yes I did reference off the same edge of the workpiece.

did you use the centering mandrel to align the router properly with the mounting plate?

Yes, I did and there was no play at all. Before tightening the screws up hard I tested for possible movement and the only possible movement was rotational which wouldn't affect the accuracy in the hole positions.

Check the space between the stop post and the threaded hole on both stops.

What I actually did check here was (using a digital micrometer) the distance between the end of the stop and the pin (or one of them) that protrudes into the hole in the rail. I got the same measurement with both stops (to within 0.1mm and I doubt if my measurement accuracy is better than this as it is difficult to make this particular measurement). I didn't perceive much play of the stops in the holes of the guide rail but what I do find somewhat unsatisfactory is that whilst you can get the stop to seat well on the rail, when you tighten up the screw, there is a tendency for the stop to cant over because it is being tightened from one side only. This would tend to move the holes nearer to the reference edge of the workpiece.  I have taken to tightening up this screw only gently so that I can make sure that when I position the rail the stop is butted up properly and at the same time, lying flat against the rail. I felt this should work as there seems to be no play of the stop against the rail when it is tight up against it and flat.

Let's say you're standing at your work bench with your guide rail parallel to your stomach and the rubber edge facing away from you.
sit your LR32 on the rail in front of you.  With the pin in one of the holes on the rail, draw a mental line square off the rail connecting the pin to the large hole in which you're centering mandrel fits

Let's say that the true center of the hole is a quarter of a millimeter to the right of your mental line.

Then you would have 32.25 mm measuring off the left, and 31.75 mm measuring from the right.

Now if your tape measure is reading long by a quarter of a millimeter, you would be reading 32 mm off the left side and 32.5 mm off the right side.

When I check the distance of my holes from the reference edge, I am using the same ruler off the same reference edge to check the two lines of holes so if the ruler had an error, it would have the same effect on both sets of measurements so that any difference in the two sets would reflect a genuine difference in hole positions. Your scenario in which you describe an error in the alignment of the centre of the 'big hole' and where the guide plate perceives the centre of each 'little hole' (I use this description to allow for the possibility that the retractable pin mechanism may not be aligned properly) would introduce errors in hole positions in opposite directions depending on whether I am indexing from the right-hand side of the rail or the left. The error would be the same in each case and the total error in hole positions (one row compared to the other) would be double this error.

If I am not mistaken, your idea of a possible cause involves making the measurement (with a dodgy rule) from opposite edges of the workpiece?

the problem is the result of how the retractable pin fits the holes in the rail.

Thats what I think the problem is.

I will do an experiment to make absolutely sure I can isolate the effect of any slack.

Thanks again for your efforts to help me out. I'll report back over the weekend.

 

[cliffp]

I've done the experiment. The difference in hole position caused by moving the router from right to left versus left to right is minimal - I would say a maximum of 0.1 mm.  To find out, I routed 4 holes indexing using the stop against the right hand end of the rail. I initially moved the router right to left applying a slight lateral force to the left to take up any play in that direction. I repeated this for all 4 holes.  I then measured the distance of the holes from the reference edge. This experiment was then repeated (again using the right hand end of the rail) this time moving the router from left to right taking up any slack by applying lateral force to the right. I measured the hole positions again. Some measurements showed no difference. Most showed a less than 0.1mm difference. I believe that if I could measure accurately enough, I would see a consistent small error that wouldn't be a concern. I also measured the distance between the end of the longitudinal stop and the centre of each hole and it was bang on in every case at both ends of the rail. My conclusion is that the error is in the mounting plate. I don't think it is the pin or pin mechanism as these seem too well engineered. I think the problem lies in the pressing of the plate - any error in the pressing could cause it to be not at right angles to the guide rail and any angle other than 90 degrees will cause a lateral displacement in the position of the drill bit relative to the centre of the retractable pin.

 

[sancho57]

Ya know, this may sound a tad stupid, but

do you have both of your stops set at 16 up and out?  If they are not the same it will throw it off.

Dont ask me how I know this  [scared]

 

[cliffp]

do you have both of your stops set at 16 up and out?

Yes definitely.

 

[bruegf]

I feel your pain, the last few times I've used my LR32 I've ended up with nearly 1mm difference in hole location and I have yet to figure out what is causing the offset.  In theory it should be impossible (assuming you've done things correctly) to end up with that much offset.  I too have checked the pieces for square, centering of the router on the base plate, calibration of stops, etc. 

If I don't figure it out pretty soon, as much as l like the LR32, I'm going to pitch the damn thing and go back to the way I used to do it.

Fred

 

[cliffp]

Fred, Thanks for the sympathy! It is annoying. I have messed up 3 panels and wasted hours investigating the problem. I am fairly confident I have isolated the problem and will ask for a replacement guide plate. I hope you find a solution to your setup soon. Surely you could ask for a replacement set and you would then be likely to solve the problem?

 

[tiralie]

Fred, Cliff
Just curious what router you are using?
I am going to check to see if I get the same results with my 1010
Tim

 

[cliffp]

Tim, I am using an OF1400

 

[Michael Kellough]

I've done the experiment. The difference in hole position caused by moving the router from right to left versus left to right is minimal - I would say a maximum of 0.1 mm.  To find out, I routed 4 holes indexing using the stop against the right hand end of the rail. I initially moved the router right to left applying a slight lateral force to the left to take up any play in that direction. I repeated this for all 4 holes.  I then measured the distance of the holes from the reference edge. This experiment was then repeated (again using the right hand end of the rail) this time moving the router from left to right taking up any slack by applying lateral force to the right. I measured the hole positions again. Some measurements showed no difference. Most showed a less than 0.1mm difference. I believe that if I could measure accurately enough, I would see a consistent small error that wouldn't be a concern. I also measured the distance between the end of the longitudinal stop and the centre of each hole and it was bang on in every case at both ends of the rail. My conclusion is that the error is in the mounting plate. I don't think it is the pin or pin mechanism as these seem too well engineered. I think the problem lies in the pressing of the plate - any error in the pressing could cause it to be not at right angles to the guide rail and any angle other than 90 degrees will cause a lateral displacement in the position of the drill bit relative to the centre of the retractable pin.

Your conclusion makes sense. It could also be as simple as a burr on the large hole in the plate that causes the router to be offset. Similarly, there could be a burr or other displacement in the channel of the plate. If you don't find an obvious and easily corrected cause then hopefully a replacement will be better.

The LR32 plate is useful but I've never used it "for fun". I'm always under deadline pressure when I get it out and any problem with the results is dealt with as quickly and directly as possible.

I did have a displacement problem once that was due to un-square panels. I just added a bit of shim between the end stop and the panel edge so the holes hit the mark. The cabinet bottom ended up slightly warped but the shelves didn't wobble.

If you keep the plate and are sure the error is in the angle of the channel in relation to the axis of the pin and router bit another option is to add shim to one end of the channel.

It's pretty difficult to check errors of that kind. The panel has to be perfect (opposite sides have to be perfectly parallel and the ends have to be perfectly square) and the a reference line has to be perfectly squarely drawn across the panel at the exactly right distance from one end of the panel. Once that is done it's easy to find the center of the hole using a center pilot bit like this.

Plunging so the center point just touches the work makes a very fine mark that you can measure to make a shim.

 

[mastercabman]

One thing you could check is when using clamps to hold the rail in place,make sure that the stops are still against the edge.
I have noticed that when I apply pressure on the clamp,the rail moves,not much but it does move.

 

[bruegf]

One thing you could check is when using clamps to hold the rail in place,make sure that the stops are still against the edge.
I have noticed that when I apply pressure on the clamp,the rail moves,not much but it does move.

Yeah, I've noticed that too, but the last couple of times I've used it I made it a point to double check, both before and after drilling the holes, even using a very thin piece of paper to verify that I couldn't insert it between the stop and the end of the panel.

Fred

 

[cliffp]

Michael, Thanks for that. Your suggestion of making a very tiny mark by just touching the bit against the workpiece to check before drilling sounds like a good idea. Whether I end up with a better guide plate or have to make do with the one I've got, I will if necessary use a feeler gauge to compensate for errors where the holes are too far from the reference edge. My experiments have shown me how essential it is to have completely square panels. My first attempt at drilling holes actually had an error of 1mm between the two rows of holes and I think half of that error was due to non-square panels. I learned my lesson after this and the experiments I described were done using square panels.

Mastercabman, On the subject of checking that the clamps have held the wood against the stops, I checked that carefully. The 1400 router is very heavy and it could easily cause things to move if the clamps are not done up tightly.