Why is it called Tramming?

No idea and simple googling does not give me a definitive answer. I cannot even say that it has nothing to do with Trams, all the wheels must be square with the rails!!

If you cut a level surface and you see that the surface is not actually level, but you can see

‘Tramlines’ or ripples along the surface then the router needs tramming! The larger the bit the bigger the tramlines left on the Spoilboard or stock, but I don’t think that is why it is called

tramming, but it is what it is and the name doesn’t matter, just the process and the end results.

What is Tramming and why is it important?

Tramming is the process of adjusting the spindle motor mount so that it is vertically aligned to the bed on the X and Y axes.

Consider the picture (it is a little exaggerated), the green is a representation of a bit which is perfectly trammed or aligned with the bed, as it cuts it will leave a level surface. The red, which is un-trammed, will cut a groove out of the stock (the shape depends on which way the bit is moving) The larger the bit the more the effect will be.

This can be noticeable when you surface a large area and the bit will leave a

‘ripple’ effect on the surface as one side cuts deeper than the other.

Unless it is really out of alignment, which is very unlikely, the importance of tramming depends entirely what work you are going to be doing, if you are just using V carving to make signs or engravings then it will be very difficult to see any difference between a perfectly trammed router and one which is a little out.

However, if you are trying to leave flat surfaces, cutting something like Inlays or parts to assemble the effects can become important.

Some terms and descriptions

What is a Dial Gauge?

You don’t need one for this but they are mentioned here, so if you know what

they are already, move on.

A Dial Gauge uses a probe to measure small changes in distance which can be read from the hands on the dial, typically accurate to 0.01mm. As the probe is

moved in or out the measurement shown on the dial changes, useful for measuring small, relative, distances. Lots of options (and prices available), mine cost me ~£10.

They can be mounted in a variety of ways, the one I am using here uses the probe holder (8mm diameter) inserted into the tramming bar.

Square vs Trammed

A critically important step to complete before even thinking about tramming the router is making sure it is square.

Square means that the X and Y movement of the router maintains a constant height of the centre of the bit over the bed/Spoilboard. In the picture the router is not square, but once the Spoilboard has been surfaced it will be square.

Trammed means that the movement of the Z axis is perpendicular (at 90 degrees) to the Bed/Spoilboard/Stock on both the X and Y axes. It’s a subtle difference but an important one. Normally the router is squared on the X and Y axes by fitting a Spoilboard and surfacing it. This will ensure the X and Y axes move over a level bed with a constant Z height at the centre of the bit.

You cannot tram the router until the bed is level/square on the X and Y axes so fit a Spoilboard and surface it first. If the router needs tramming this can be an iterative process, surface, tram, re-

surface…. To get it as accurate as possible.

Runout

This effectively is the measure of any wobble on the motor as it rotates. Think of a bent motor shaft, as it is turned the ‘bend’ will move from side to side. This distance is the runout. You are only going to be able to measure this using a Dial Gauge. Mount the probe horizontally and measure the side to side distance of a round bit as it rotates 180 degrees. The maximum movement is the runout.

Practically this should be very small, unless something is faulty it can be ignored. You cannot successfully tram a router which has a significant runout. It is unlikely that your router has significant runout. A visual check will normally be adequate.

Tramming bar

Think of it like a magnifying glass for distances, it fits into the spindle motor collet at one end and the other holds a Dial Gauge or something that rubs along the surface of the Spoilboard like a bit. As it is rotated the end will move up or down relative to the surfaced Spoilboard so you can work out where and how much the angle of the spindle motor needs to be adjusted. The picture shows a single ended Tramming bar rotated through 180°.

It doesn’t have to be fancy or expensive to do the job well, it just needs to keep its rigidity as the spindle is manually rotated, it can even be springy as long as it holds its original shape so a bent coat hanger will work.

Some examples and ideas are listed below, some need a 3D printer to make.

The size of the router is also important, the longer the bar then the more it will amplify the distances, but it also needs to touch the surfaced area of the Spoilboard all the way round, so if you are tramming a 3018 then a length of no more than ~89mm is usable.

Lastly are you going to use a Dial Gauge or a bit?

• Using a bit just touching the bed scrapes along the surface as it is rotated so you can tell where it is lifting above the bed or being pushed further into the bed. A ball nose bit is preferableas this will not stick into the bed as much as a V or flat end bit, but you have what you have. If you are using a V bit think about mounting it upside down but be careful of the sharp end sticking out!
• A Dial Gauge will give you height readings as you rotate the tramming bar which is more accurate.Unless you already have a Dial Gauge, I would not buy one for tramming a small hobby router.

Some Tramming bar options are:

Universal Tramming Bar

3D Printed, fits in a 6.35mm (1/4”) collet, takes an 8mm Dial Gauge OR 3.175mm (1/8”) bit. Two sizes, short - length 87mm for bit, 80mm for Dial Gauge or long - length 147mm for bit, 140mm for Dial Gauge . 

OK it’s a pretentious title! Designed to fit small routers (3018 and above) these will both take a Dial Gauge with an 8mm diameter probe casing (the round part that the probe pushes into) or a 3.175mm bit. There is a mount for an M4 clamping bolt should it be needed but both the bit and Dial Gauge should be firm enough without it.

Use the size appropriate for your router, it must rotate to be above the surfaced area of the bed and also not foul on the Z frame as it is rotated (only applicable if using a dial gauge)

James Deans Designs Tramming bar

3D Printed, fits in a 6.35mm (1/4”) collet, takes a 3.175mm (1/8”) bit. Two sizes, length 120mm or 180mm. Download Here

Designed for larger routers with a bed size greater than

240x240mm and takes a 3.175mm bit as the probe. There is a clamping hole but a 3.175mm bit should fit well enough without it.

Allen Keys (My thanks to James Dean Designs for the idea)

Collet – variable, Length – variable.

Two Allen keys attached together as in the picture, A very simple and cheap design but effective. They do need to be held together

securely, taped, tie wrapped, glued, welded (perhaps gluing and welding is a bit much). A 2.5mm Allen key will fit into a 3.175mm (1/8”) collet, a 5mm one into a 6.35mm (1/4”) collet. The lower key does not have to be the same size as the top one.

How to Tram your router

Make and fit a Spoilboard and surface it!

You can only tram a router above a square/level bed. If you are going to engrave the Spoilboard with alignment lines perform the tramming before the engraving just in case it needs re-surfacing. If the Spoilboard is ‘well used’ re-surface it first, if it is uneven then accurate tramming will be difficult if not impossible.

For safety tramming should be done with the power to the Router OFF or at least the motor disconnected to prevent it trying to accidentally spin the bar which could be both dangerous and disastrous.

Attach your tramming bar into the spindle motor, it needs to be securely held, but does not need to be as tight as a bit, finger tight or just a little above will do.

Position the spindle on the X and Y axes to where you want to measure, normally the centre of the bed, making sure that the end of the tramming bar is over a surfaced area of the Spoilboard throughout a full rotation. As the power is off manually turn the Z axis leadscrew to adjust the height.

• Ifyou are using a solid bar or bit then adjust the Z height so the end of the tramming bar just touches the Spoilboard surface.
• If you are using a Dial Gauge then set the Z height so that the probe is depressed by say 1mm.Note the readings on the gauge as you rotate  A Dial Gauge should be accurate to 0.01mm (0.0004“).

While tramming be sure of what you are measuring, there are some do nots to observe

• Donot rest your hand on or apply any force to the router bed, there will always be a slight movement of the bed if it is pressed down, not a lot but that is not what is being
• Donot rest your hand on any other part of the router for the same 
• Donot move the motor spindle up or down when rotating the bar, there will always be a little play in the spindle so keep the forces horizontal.

Even if you have a dial gauge, I would start off by using a bit in the tramming bar, it’s easier to adjust

as the dial gauge has the annoying property of being difficult to read all the way round.

Manually rotate the tramming bar. You can tell as it rotates if it will want to dig down or rise above the Spoilboard, ideally it will stay just touching, or at the same height above for a Dial Gauge, the Spoilboard during a full rotation. If it does this your router is perfectly trammed!

If it doesn’t, then adjust the router to change the angle of the spindle relative to the Spoilboard. If it is lower at the left but higher at the right you will need to rotate the spindle motor on the X axis clockwise a little to level it up. The same applies for rotating the motor on the Y axis if the height varies front to back.

I would suggest picking the axis which is most out and adjusting that first, then adjust the other axis. I have found that trying to adjust both the X and Y axes at the same time is much harder than adjusting one at once.

I would normally re-surface the Spoilboard by a small amount after tramming to remove any tramlines. Not that it will make any difference to the efficiency of the spoilboard but it is a useful way to see the difference tramming has made and if further effort would be useful.

Note it is very difficult to get comparison photos, the way the tramlines appear depend on the angle and lighting conditions but I think this is a fair comparison.

1 Surfaced, before Tramming

2 After Tramming and re-surface

Then recheck the tram, it should be better!

Making Adjustments

The adjustments are going to be small, sometimes minute! If your tramming bar is 100mm from probe to centre and the height difference between the ends is 0.5mm then the angle needs changing by ~0.15° which is not a lot!

Once it has been trammed the router should not need adjusting again, however it’s worthwhile checking periodically. However, if you change something like the motor mount then re-tram it.

What you can adjust depends on your router, smaller ones such as 3018s tend to be more limited as they usually have a fixed motor mount/Z Frame which does not allow any easy adjustments for tramming on the X axis.

The larger routers tend to have bolted together motor mounts and Z frames rather than a one piece moulding which means that there are more possibilities for adjustment.

The following table contains my suggestions on what should be adjusted first, depending on the router. More detailed descriptions follow.

^*I don’t have one of these so how to adjust is based only on the User Manual and other descriptions available online.

I have actively tried to avoided shimming anything, the adjustments needed are likely to be small and using the little slack available in mounting bolts is easier and should cover the necessary movement.

NOTE: When slackening bolts do so just enough to allow the component to be rotated slightly, leave one tighter so it can be rotated about that bolt to maintain any X and Y positioning.

After any adjustment re-check the tram, tighten the bolts then re-check the tram again!

Rotate Gantry

Use this method where the X axis at the top of the gantry is in separate components such as extrusions and guide rods which are secured to the gantry independently. The adjustment of these is more about making the router free running and square.

This adjusts angle of the whole gantry to the bed frame. Slacken the bolts holding the gantry base to the frame. Rotate/tilt the gantry on the Y axis

to adjust the angle the bit will make on the Bed. Both ends of the gantry will move slightly independently so be prepared to adjust each end accordingly.

NOTE: Raising or lowering the gantry height at the ends will not rotate the Z axis in relation to a level bed along the X axis, it will just affect the square of the X axis to the bed.

Rotate X Frame

Similar to Rotate Gantry but for routers where the top of the gantry mounts a single frame along the X axis. Slacken the bolts holding the frame at the top of the gantry and rotate/tilt the frame on the Y axis to adjust the angle the bit will make on the Bed. Both ends may move slightly independently so check the tram at both ends of the X axis and adjust each end accordingly.

NOTE: Raising or lowering the gantry height at the ends will not rotate the Z axis in relation to a level bed along the X axis, it will just affect the square of the X axis to the bed.

Rotate Motor Mount

If the motor mount is bolted onto the Z Frame the bolts can be slackened and rotated. There are two possibilities here, the motor mount has a flat base and is bolted to a flat frame, this means it can be rotated around the X axis to adjust the Tram. The 4040 has a bolted on motor mount but the bolts are at the sides. This means it can be rotated on the Y axis but not the X.

Rotate Z Frame/Motor Plate

Where the Z frame is bolted to a flat mounting plate such as on the 3020 but has a solid, fixed, motor mount the bolts holding the Z frame/Motor plate can be slackened and rotated around the X axis.