Tramming, an excercise in futility

I got into a discussion last week about tramming the longmill, during which I had stated that though I knew that my router was not square I saw no need to tram as visually there was nothing noticeable in the finished product. I ended my part in the discussion by saying that I would go ahead and complete a tram, which I did this past Saturday. I set and levelled a suface plate (piece of glass) on the spoilboard. I then checked the x axis for square to the plate, the rail was leaning backwards by about 0.025 in. I eventually got it into square by multiple wheel adjustments of the x axis to y axis gantries. The issue being the adustment of the wheels to achieve the squareness required was so close to overtight and causing a racking motion of the x gantry leading to jamming. At this point I campleted tramming with side to side being out by 0.0002 and front to back out by 0.006. Seeing no need I did not attempt to adjust either of them. At this point it occurred to me that I should simulate the forces on the router when in use. Not being sure what the actual force would be I presume it would involve the torque of the router, feed rate, cutter diameter, and material density, though that would be a seperate discussion from this. I decided that 10lb would seem to be a reasonable force so using a spring balance i appled 10 lb at a cutter in the collet, along the x axis the deflection was 0.024 and fore and aft it was 0.082. So this is where I am convinced that doing a tram is a uneeded excercise that will not result in a superior performance than if you just get the rails square to the bed as it is not possible to get the spindle mount rigid enough to prevent deflection when in use. This is due to the fact the wheels cannot be tightend sufficiently without locking up the machine.


@Mickus An interesting perspective, Michael. I’m on record here as being at odds with many users. That does not make any of us “wrong or right”. I have never measured the tram on my Mk1, nor have I ever applied a static force to the router to measure deflection. I know that Sienci has and has reported on it. I simply never saw the point. Clearly, deflection will vary between machines and on the same machine. A 1/4" end mill cutting hard wood at an aggressive feed rate will deflect more than a 1/16" tapered ball nose doing a final pass on a carving. Of greater influence, I believe, is how the router is mounted. Some time ago, an engineer whom I respect was milling aluminum on his Mk1. He demonstrated clearly that raising the router as high as possible in the router clamp resulted in much less deflection that having the router as low as it could be in the clamp. Even for a non-engineer like me, that made sense. The leverage exerted on the router mount with the router low was much more than if the router were mounted high.
I tend to look at this within the context of the projects that I run. If I am satisfied with the end result, the machine is set up accurately enough. I don’t wait to be dissatisfied before doing routine maintenance, including any necessary adjustment to the vwheels and anti-backlash nuts. However, if all looks good, I just keep on carving.

I came to this as a woodworker. As I nauseatingly-often say, “wood moves”. I do many picture frames. I start with rough-sawn lumber, mill it, then carve it on the Long Mill. I have seen glue up frame blanks twist more than an 1/16" over night. These are from kiln-dried lumber kept in my basement shop for a long time to acclimate. Worrying about the Mill being out a couple of thousandths of an inch simply does not enter into the equation.

Here endeth the sermon. Thank you for posting your observations.


After reading both previous posts, I can’t help but be reminded of a certain video we’ve all probably seen of someone standing on the X axis and jogging around. What does that prove? I always wonder, I guess it means that the plastic feet are pretty strong! Stand on the router and I’ll be impressed!

Don’t get me wrong I really love my LongMill but it doesn’t take much force applied to the router to see deflection. I think that if the machine was stiff enough for me to not see the deflection, I wouldn’t have been able to afford it. :upside_down_face:

Thank you both for your perspectives on tramming.


I have absolutely no issue with my 48 x 30. I got it this past January and have been more than pleased with the purchase, I think it is good value for the price paid, does what I wanted it to do, carvings, and the finished product is superior to what I can achieve after years of practice with hand tools. The point of my post is no matter how well the machine is trammed there is still the deflection issue to contend with, along with, as @gwilki mentions wood movement which has to be accounted for when we make stuff. I work along the lines of if it looks OK then it probably is. As for machining metals I would agree that it is possible but tolerances would have to be adjusted. This is a hobby machine that is well engineered and built and priced very competitively. Had tight tolerance been on my list I would have been looking at machines costing significantly more than I was willing to spend. I had no intention of completing a tram being of the opinion that it is not necessary. On that my opinion has not changed. @_Michael I have not seen what you mention but the macine is strong enough, though as you say why?


I’m a little confused by your post and procedure. I would never use the wheels to adjust the tram of the machine. That doesn’t sound like it’s good for the longevity of the steppers since you can’t adjust them in opposing pairs. Adding resistance to the work the motors are doing is a recipe for disaster.

It’s cool if you never found the need to tram your router and it never impacted your work product. When first assembled, my machine was dead flat parallel to the gantry when surfacing with a 1" bit but probably leaving rows of 1/32" to 1/16" deep lines perpendicular to the gantry. You could see and feel them. It needed to be trammed or else when I go to flatten a piece of nice wood I’ll be sanding it into eternity to remove the resuting ridges left behind.

The solution was loosening up assembly screws and twisting the router to the extreme opposite of the direction it was off, almost to the limit. That took care of it. Now it cuts just about dead flat.

It’s not neccesarily futile if you know what you’re trying to accomplish and you are adjusting the right parts to accomplish it.

I’m also not sure you’re understanding the purpose of tramming a machine. It doesn’t mitigate deflection, it mitigates tolerance stacking. If your spindle is off axis say, .05 -X (not how it’s measured but we’ll think in 2d for a minute) and you’re deflecting .05, not only will a shape, let’s say a circle, be oblong along your X axis, it won’t be flat on the bottom. If properly trammed, you’re only dealing with deflection and not also the tilt in the spindle. If you make a circle box and a matching lid, unless you build in enough slop, they only fit along one axis because of this tolerance stacking.

It might not matter for many processes but will for some. In reality, tramming impacts 3 dimensions, as cutters aren’t flat planes, so the closer the axis of the spindle is to perfectly square to the machine bed, given good, consistent tooling, the more predictable your cuts are going to be compared to your design.

Again, it might not make a difference to you and that’s cool. It doesn’t have to. Don’t dismiss a process simply because you don’t benefit from that degree of accuracy or understand the value.

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@CncJim it all started from a posting last week regarding surfacing prior to tramming, during which I mentioned that although I knew that my router was not perpendicular to the bed I saw no need to tram, but said that I would go ahead with the excercise. I adjusted the x gantry wheels because I found the x rail had a rearward lean and getting it square would probably result in less shimming when I completed the tram. All x gantry wheels are turning but getting to the point where the wheels were not overly tight and the x gantry was squared took a lot of time and frustration. In the end I did not attempt to adjust the router as it will not be possible to see cuts out by 0.0002 and 0.006 no matter how much tolerence stacking. I primarily purchased for carving and in that regard I am very pleased. For other wood cutting operations I have a large workshop full of tools that allow me to do these other operations more quickly and perhaps that is why some it seems are convinced they need to be trammed perfectly.

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I dig it. For me, I’m looking at flattening slabs too large for my thickness planer and cutting guitar bodies. Other times I want to cut and mill very precise joints… dovetails even, so tight that one would have trouble believing that they weren’t hand cut.

In my shop, my CNC allows me to run jobs like this while I set up other stuff and/or provides repeatable results I can’t always count on manually, in much less time.

To do these things, I need to know that I have controlled whatever variables I can. As you well know, wood gives you enough variables you can’t control, no need to leave anything to chance if you can help it.

All things considered, it sounds like with your wheels adjusted, your LM is pretty damned accurate. I wouldn’t personally tram a wood CNC much past .001, and I would only bother going that far if I was adjusting it. I certainly wouldn’t check a machine just to make sure it was that good. I think I managed a little better when I adjusted my machine but it was just how it worked out as I was using a 6" tramming beam.

In the end, what matters is that the machine is producing the product you are happy with. Sienci says the LM doesn’t require tramming. My still very limited experience says at least some LMs need to be trammed at least after initial setup. Every CNC I’ve owned has needed it and, honestly, the LM was pretty easy, especially compared to my Bobs CNC. With luck, it’ll hold the positions well and never need it again. If cut quality suffers or when I change the wheels, I’ll check it but it shouldn’t be a point of obsession.

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