Troubleshooting Out-of-Square Moulders

      Follow the saga of a woodworker trying to solve the puzzle of not one, but two, out-of-square moulders on the shop floor. April 30, 2009

We have a P26 and a Unimat 500 and run standard square cap mouldings (L shaped) with a 1/4" rabbet on the top head, straight knives on all other heads. The problem is, on both moulders the right side head seems to tilt in at the top (2" head) causing things to be out of square. I grind on a Rondomat and check with an Opti control measuring system. Everything says it's not in the tool room.

Am I missing something? Both moulders are doing the same thing. But to get something square out of one of them, I have to shim the template and grind the knife on a slight angle to compensate for it. I have checked the heads (which are new) and there are no burrs or any dings that would cause any problems. Can anyone think of anything else to check? The bedplate is square to the fence (after the first right) but the straight edge hits light on the bottom and super heavy off from the top of the fence.

Forum Responses
(Solid Wood Machining Forum)
From contributor C:
Take your first fence head off and check the spindle for square to the bed plate, and how the bed plate sits to your first bottom. If itís out of square/level, then the bed plate needs attention. Check that the spindle is running true with no discernable difference when you rotate the shaft. Check it in four spots, not just one, or better yet put an indicator on it.

I'm not familiar with the Weinigs, so perhaps this isn't the case, but the bed plates on my Sicar sit on adjustable posts to level and square to each head. The fence actually sits/attaches to the bed plate so there is no adjustment there except for shims or grinding, but shouldn't ever need it as it just sits on the plate.

Underneath the plate, look for the bed plate mount and see if the mount itself has some sort of two piece construction or cam action to raise and lower the bed plate. If it is just bolted to the main casting, you can loosen the bed plate bolt(s) around your first side, and using shim stock square it to the spindle, not a head. Or, I've seen the spindle housing shimmed, which I don't like as those mounting faces should be referenced to the main casting for level.

If you do this, make sure you keep an eye on how your adjustments affect your first bottom as well. If you are square across the 1st bottom, adjusting the bed plate will throw that off, which just moves your problem.

As a last thought, a call to tech support is probably your best bet, as playing with all this stuff can open a nasty bag of snakes that will make you pull your hair out for a long time till you get it fixed.

From Dave Rankin, forum technical advisor:
If both moulders are doing the same thing, it may be in the alignment of the grinder. It also may be the template that you are using for the right cutter. It is not common for two moulders to have the same problem as you are talking about unless there is an issue with the grinder.

From contributor A:
After doing your test where you are hitting light on bottom and heavy on top, try turning your head upside down and performing the test again. If itís your tooling then your results will be opposite.

Another thought is: how are you holding down this moulding with the pressure shoe after the #4 rabbet cut?? If you have the pressure shoe on the top of the L shape then it may be pushing that side down further into your #5 bottom cut. This could be causing it to be out of square. If your pattern will allow, try adjusting your pressure shoe so it rides in the rabbeted out part of the cut.

From the original questioner:
My first thought because it is an issue with both moulders was it had to be in the grinding part. But we now have an opti-control measuring stand Ė kind of like an overhead projector. It shows (even on our 9" heads) that everything is perfect. We even bought a new template for straight knives and the problem is still there.

Our U-500 is only about a year and a half old so worn bedplates shouldn't be an issue. I have checked the first bottom with the straight edge all the way across and all is good. Most of our L shaped mouldings only have a 3/16" lip so we ride the pressure shoe inside the rabbet. A typical width is 1-1/2"-2". We run everything through a profile sander but have to do it twice just to square things up.

I ran a piece in all the way and shut the machine off, pulled the piece out and the out of squareness starts with the first right side. It's a head scratcher! We do have a veteran Weinig tech coming soon.

From contributor R:
One simple but accurate way to get you started in the right direction might be to get a good machinist square. Get the right spindle bedplate as close as you can to the spindle with no head on it. Put the edge of the square on the bedplate and the other edge of the square up to the spindle itself. With a feeler gauge try and slide the gauge between the square and the spindle shaft, and also try it between the bedplate and the bottom of the square. This will let you know just what is out of square. I have seen worn bedplates in a short period of time from the customer's running the same profile's over and over. Just a thought to get you in the right direction, you seem to have the other things mentioned eliminated, good job troubleshooting!

From contributor R:
I forgot the most important part! Contributor C's post is what lead me to my response. I think he is on to something here. Try what we said with the spindle belt off first. Then put the spindle belt back on and try it again, see what happens.

From the original questioner:
We have a few of those machinist squares. I plan to check that out. I'm curious about how it would be different with or without the belt on. Is there enough play in the spindle housing to have belt tension move the spindle?

From the original questioner:
I forgot a trouble shooting update as I am now addressing this problem. I finally got a square blocky type profile "square". After several attempts, and nine pieces of masking tape(.037") to shim the right side of my template, the straight edge hit equally top and bottom from the fence and the end product was square. Interestingly enough, before running any wood, I took the head off and put it on the U-500 and found it was "over" corrected for that spindle. So at this stage, both moulders have the same problem, but don't seem to be the same amount out of alignment.

The other thing I forgot to mention is the left side spindle is tilted in as well. I checked on a piece of s/4/s stock. That doesn't bother me because that is generally the bottom of the profile and doesn't matter but might help you guy's with a diagnosis of my problem.

From the original questioner:
Well, the first thing I did this morning was take the side heads off and check the spindles with a machinist square. Low and behold here is the source of the problem. The left and right spindles both tip inward on both moulders. So thank you all for your help finding the culprit but this raises yet another eyebrow.

My boss reminded me about our first moulder years ago - a P23. When we traded it in, Weinig said that it was because of the welded steel frame they used back then. The moulders we have now have a cast iron frame and sit level. Is this a common thing for non jointed Weinig moulders or am I doing something to cause this problem? The spindle housing is cast also so no shimming can be done.

If anyone has heard of this before, I would love to hear about it. I know people can develop bad habits over time so I can't help wonder if this is because of something I'm doing. If so, I need to know. My first thought was worn spindle housings because I wasn't greasing enough. But if that was the case, the tension from the belts would make the spindles tip outward.

From contributor L:
I run insert heads on the left and right side spindles on a Unimat 300, which is pretty similar to your 500 and had to flip inserts this morning so I pulled the heads off and got out the machinist square and checked the perpendicularity of the spindle to the table and they were spot on. I know this doesn't help much, but you wanted someone else to take a look at theirs. I'll be looking forward to hearing how things work out for you.

From the original questioner:
The past couple days I have done a few experiments when able. At this point, I believe the spindles are fine and the bedplates are worn. It surprises me if that is the case on the U-500 but the P-26 I'm pretty sure thatís the case. By grinding on an angle (right side) I can square up a profile over 2" wide. Anything under that is out of square. We run a lot of skinny mouldings (worn bedplate by last bottom close to fence).

From contributor R:
Just a thought for the next machine you order. Spend the extra money and get the machines bedplates chromed. That is what the Precision Metal will do, grind them level, then chrome plate them. You probably not wear them out again if they are chromed. Some manufacturers are now selling their machine's chromed bedplates standard, no extra cost. This is a big plus in the price of the machine when you compare apples to apples. To prolong the life of your bedplates now, metal rollers no more than 40psi and rubber rollers no more than 30psi. Use lots of lubricant on the bedplates, make the setup fences, pressure shoes, and chipbreakers, as light as possible. I hope this helps you a bit till you can get them fixed.

From the original questioner:
I have faxed them in the past looking into rebuilding an old 22N.I'm sure we will use them if they decide to fix this. This has been a fun troubleshoot. I just wish I wasn't so busy during the day to devote more time to it at once. My boss is the kind of guy that can figure anything out. He is either just waiting for me to solve this, or he has too much on his plate right now to deal with it. Either one is a probability, but it might be a few days before anything happens.

From the original questioner:
With the straight edge off the fence, it shows the spindle tilted in. If the fence was warn, it would hit heavy on the bottom and light on the top? Grinding to make the straight edge hit evenly would allow me to get square product wider than 2". Without grinding on an angle on the right with a width of over 2" it's not square.

From the original questioner:
I was running the U-500 today and ground the knives on the right side (2" head) so the straight edge hit evenly off from the fence top and bottom. I had to run some birdseye maple so I lowered the head to use some sharp steel and checked it (straight edge on the bed against the fence) and it was at least .005" away from hitting the straight edge. I cranked the head in until it just rubbed, and cranked the head back up to around .394" where I started and it hit heavy. The U-500 is to new for bedplate wear. Just bringing the head up and down makes a difference on how heavy the knife hits the straight edge (with the same reference point). I'm not good with geometry. Does that make sense if the spindle is tilted in like the machinist square shows? Almost like lowering the spindle is "backing it away" from the fence?

From contributor L:
If the spindle was tilted in and you lowered it, the opposite would happen. As you lowered the spindle it would start to hit hard, or take more material rather than less.

From the original questioner:
I figured out today that what was going on was indeed because I ground the knife on angle causing that result. We also today confirmed that the P26's problem is worn bedplates. It is a lot worse than expected, so now that machine is out of the equation. But the U-500 showed no sign of ware.

The other thing I learned today on a square blocky type moulding is that by grinding with a .020" shim under one side of the template, it squares the right side of the moulding to the bottom but makes it a little out of square to the top. Although the machinist square clearly shows the spindle tipping in, it leaves me to think there might be an issue with the pressure shoe or last bottom head. Little by little but were honing in on it.

From the original questioner:
Well, it's over. I was able to play around a little today and chased the problem to the last bottom head. That's where the out of squareness started. I found the pressure shoe not parallel to the bedplates. It was pushing one side of the moulding into the cutter head harder than the other causing out of squareness. No matter what the square was telling me, the side spindles are fine. So the 500 is running like a champ again.

So thanks to everyone for the help! It's been fun, educational and a little embarrassing. The problem was right under my nose and I started way out in left field convinced that was where it was. A wise man once told me,"98% of the time it's something simple. Knowing where and how to look is the key." I took me a while but that proved to be true once again. It was a good reminder of just that.

From contributor R:
Glad to hear you got the problem solved. A good way to check your square for being true is this. Put one edge of the square against something flat. Draw a line on the edge of the other edge of the square. Now flip the square over and check it against the line you just drew. If square it will line up perfect. Just a thought on if you square is true or not.

From contributor R:
Sorry I missed out on this interesting discussion. A couple of simple suggestions which could have found the problem sooner:

1. Check grinder/template accuracy by measuring diameter at both ends of head.

2. Have two precision machine squares available to prove spindle / feed alignments.

3. Check table/fence alignments to tool body to eliminate possible knife/grinding errors.

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