Tramming the longmill in the y direction

The router mount tram is off in the front to rear direction. can anyone tell me how to adjust that? it’s good in the X direction but off over a mm in the Y direction?

@DCNC Welcome to the group, Darryl.

Do a search on “tramming” and you will see a dozen or so threads on what others here have done.

Thanks. I didn’t find anything regarding the direction mine is off.

@DCNC I’m probably missing something since my search revealed many posts that suggest shimming with thin metal of some sort to correct “nod”. Are we talking about the same thing?

If not, explain how you are determining that it is off by over a mm in the Y direction.

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Yes we’re talking about the same thing I believe. It’s like the top of the router is tipped slightly to the rear of the machine. I must have missed the post on shimming. I considered that but wasn’t sure it was a good idea. I’ll have to look closer to get a idea of placement. Thank you so much for your response. I’m a total newbie here at this exciting world of CNC.

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Just to check, have you surfaced your spoil board yet? If you haven’t you should do that first to make sure that 1mm isn’t in the table or spoil board.

@DCNC Just for my info, when you say that it is out by 1mm +/-, over what distance is that and how did you measure it?

Yes spoil board is surfaced and that was how I noticed the issue. the cut left a defined ridge as it traveled through the surfacing. I used a new square to check and a friend slid paper under it until the gap at the board was filled. we then used a micrometer to determine the difference so I might be off a fraction but very close. I see shimming is the only real option but where to place it is now my question. Behind the mount at the Gantry? Surely around the router isn’t a sound plan…???

And thank you for your assistance with this. I’ve been in wood working for 30+ years but feel like I’m totally lost here with this CNC stuff. Complete newbie and really appreciate any tips and advice I can get!

That’s how I noticed. There was a defined ridge in the cut left during surfacing. It sanded out easily but in a carve it would be noticeable and not as easy to sand out.

@DCNC I know the feeling.

I’m still curious about what distance you measured to determine that you are out my 1mm. To be clear, I assume you took two readings perpendicular in Y to each other. So, for example, were those readings at 12" from the centre of the router, so a total of 24" apart? And, the height difference between those two was 1mm?

I’m not trying to be argumentative at all. I’m the odd man out here in that I have never trammed my router and never seen the need to. Maybe I’m lucky. However, unless my reasoning or math is wrong, I figure it this way. Let’s say that I did measure the nod at 24" and it came out to be 1mm off. If I use a 1/4" end mill to carve something, that 1mm at 24" would translate into .0004" across the diameter of the bit. If I use a 1/8" ball nose, which I frequently do for 3D carvings, that would translate into .0002" across the diameter of the bit.

It’s not for me to say if this is acceptable or not. In fact, maybe someone here will show that my thinking or math is wrong. All I know is that I have been able to do some quite intricate two-sided carvings with my Long Mill, and I somehow doubt that I am the only one here with a Mill that is perfectly trammed out of the box.

All that drivel said, you may want to try some projects before you take much time to get your tramming perfect. If you see that the tramming error is causing you grief, there will always be time to fix it. Finally, as a long time woodworker, you will no doubt agree that wood moves even as we are milliing it. I would be willing to bet that the oak picture frame that I carved this morning moved more than .0002" from the time that I started the 4-hour carve until I finished it.

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wilki, it was that far out at 5.5" from the front and rear of the router. so if you measured out 24" in either direction from bit center that would increase the off set? Am I thinking correct? I say that because when I used a 12" square it increased the difference by about double. And you’re probably correct about the carve as the bit itself isn’t going to show that much difference in the carve so I’m likely being to anal here but being new I don’t want to get started on the wrong foot and regret moving forward prior to addressing and correcting any issue I find as I set up for the first project. I do appreciate your input a lot.

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@DCNC I believe you are correct, if you were out 1mm at 5.5", you would be out more the farther out you go.

I did not want imply that you were being anal. As I said at the outset, I am the odd man out here. Like you, I have been woodworking for a long time. I see wood movement all the time. I am in this as a hobby. I want it to be fun. Fun for me is not trying to correct an “error” of a few ten thousandths of an inch. For others, only perfection will allow them to have fun. Each to his own.

As I also said, as long as the projects that I want to do come out as I want them to be, I’m happy. If they don’t and I find that the problem is caused by the Mill being out of whack somehow, then I’ll address it.

Take care. Have fun.

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Perhaps I’m confused also, but where did you get 5.5" from? Are you trying to tram your machine using a square held against the router body? It might be worth making a traming beam and using a plate of glass so you know you’re adjusting to the motor axis, which may not be true to the router body. You can essentially get it to withing thousandths in any direction within the limits of your plate of glass, which tends to be dead flat. YouTube has some good instructions for doing this with other machines and you can adapt to using those techniques with the Longmill. You could also buy a tramming gauge set for about $100. Might need it once a year if that but if you want near perfect accuracy that’s the way to get it. I see tramming like I see guitar playing… we spend half our time tuning our guitars and the other half of the time playing out of tune. You will never achieve absolute perfection but have to figure out where your happy medium is.

You can also get some of the tram out if you loosen the gantry to side plate screws and twist the gantry forward or back and retighten.

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Slightly of topic but I am not sure I understand why you would surface the spoilboard and then tram? If the purpose is to square the cutting head to the work surface, then if they are out to begin with they will still be out after surfacing and all that has been achieved is the generation of sawdust. To tram correctly one would need to first set a level surface on the bed and then complete the traming operation using that as the reference, and once complete go ahead and surface the board.
The root issue seems to me is that we construct the machine bed using materials that are not completely flat and use construction tools (level with bubble) to determine if the table is flat, at which point we then want to achieve precision at the cutting bit. Like Graham I have not trammed the head, mine is slightly out front to back as evidenced by a slightly wavy spoilboard, However this is not visually noticeable in the finished product. Also we are working with materials that will change dimension over time.
From the description if you cannot move the router back and forth by hand you need to shim the router mount. If not using precision tools i.e. dial indicator it will be somewhat of a trial and error operation.

@Mickus I’ll take a stab at answering your question and make an observation.

    • Why surface and then tram?
      Think of it this way, there are two geometric planes in play here. The router without Z movement travels around on plane 1. The spoil board is plane 2. These two planes need to be parallel to each other i.e. equal distance along the Z axis everywhere. So the reason to tram first is to make sure they are parallel. Yes you will have visible lines if it’s out of tram but overall the two planes should be parallel after surfacing. Then you can tram and surface again, this second surfacing only needs to take off the lines, most likely less than 1mm. Hope this makes sense, it’s not the easiest to explain. If you tram first you may be tramming to a spoil board that is not parallel to the machines plane.

    • You mention level a couple of times and bubble level.
      You may already know all of what I’m about to say but it’s not clear from your post so I’ll say it. You can only rely on a bubble if you have used it for every step of construction. Meaning the table has to be level and the machine on the table has to be level. You can use the level as a straight edge to check for flatness and that my be what you meant, I don’t know.

That’s my understanding of things. Hopefully I explained it well enough, especially point 1.

Michael, I fully understand what we are trying to achieve with tramming. I still stand with my point that surfacing first is not needed. Consider a overhead milling machine with a cast iron or steel bed that has been surfaced flat during its construction. During install a concrete machine bed would be levelled with normal bubble levels, when setting the machine it would be levelled on the pad with a clinometer and shimed level. In use the head would be trammed level to the bed using a surface plate and dial indicator. In our case we want to achieve the same outcome have our Z perpendicular to the bed. So by setting a reference surface to the z and setting z perpendicular to our reference we can now surface the bed knowing that we will be parrallel and square. Surfaceing then tramming and surfaceing is an extra step not needed.
My point about the bubble level is that it is not a prescision intrument and is open to interpretation by the user depending how it is viewed.
Again I personally think that in the majority of cases tramming is not normally required as most users will not need the precission attaind by tramming the head. And when I eventually replace my spoil board it is unlikely that I will bother with surfacing it.

I’m sorry if my post came out wrong or I was explaining stuff you already know. With people at different skill levels and backgrounds I’m sometimes not sure at what level of knowledge to write at if that makes sense. After reading your response and rereading your first post I think I may have misread the part about the bubble level the first time.

I agree with this, I checked my LongMill just in case and it was and is close enough for what I use the machine for, wood only so far.

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Michael I did not take your reply as demeaning or negative in any way. Just voicing my opinions, which are subject to change, if I can be so persuaded. I enjoy the back and forth, and glean knowledge from other peoples perspective. Having read a lot of your posts I have found you have well reasoned responses over a variety of subjects.


I tram my machines and I had to tram my LM. It was a fair amount out at 1" when i surfaced my spoil board so i broke out the beam and plate and it was about .125 at 12" across X. That’s a lot. My experience has been that I hate sanding lines out of my pocket cuts so I adjusted it.

I doubt it came close to perfect but I stopped somewhere around .01 in 12". If the LM was set up to tram and I hadn’t had someone borrow my tramming gauge I suppose I could have wasted some time shooting for perfect but I probably wouldn’t have seen the difference in performance.

Ultimately, I think it depends on what kind of milling you do as to how much your impacted by bad tram.