Calibrating a CNC Spindle

Tips on how to adjust a CNC spindle for accuracy. August 29, 2014

Question
I want to check my CNC spindle for accuracy and I was wondering what the method is for this and what kind of gauge I need to use or get? I would normally hire a tech for this, but there is no one in my area.

Forum Responses
(CNC Forum)
From Contributor W:
When you say CNC spindle, are you wanting to check tram on the spindle or actual resolution as in distance and square?


From contributor T:
Where is your area? This depends on the type of machine as well as the options equipped. Most flat tables would only be mechanical perpendicularity and positioning. If there is a boring unit or multiple boring units they would need the above checked as well as alignment to the router or multiple routers if equipped. If it is a pod and rail style, then not only is all of the above critical but pin alignment to the above and to existing other multiple origins becomes critical. It is never quite as cut and dry as everyone would like to believe.

From contributor O:
A bar ball tester is quiet an investment but is the most accurate method to check your machine. Or you could sweep the tram with an indicator on an extension out of the tool holder. It just depends on what you want to check and how accurate you need to be.

From the original questioner:
I have a SCM CNC and I think the spindle is a little bit out of plumb in the y axis. So when you cut down the x axis the cut is a fraction off!

From Contributor J:
Run a good 3-4" flycutter across your MDF spoil board. Do one program in the X direction (whole panel), then one in the Y. Note the ridges, adjust the spindle to remove them in the appropriate direction.

From contributor Z:
I work on lots of different CNC machines and I carry a PRO TRAM with me. It works great. I can true out a spindle in less than an hour as long as the spindle bolts are easy to get to. I think I paid about $120 for the unit. It’s worth every penny!

From Contributor U:
Be careful with your machine. Aligning the spindle on a woodworking machine is similar to a metal machine but there are some big differences. A woodworking machine's base is more flexible than a metal machine because it is lighter weight.

You will want the right spindle alignment tool and base. You level out the base first and then you align the spindle to the level base. If you have a flat table machine, the table can be off compared to the spindle. This is normal especially with using the spoilboard. That is why you use a perfect machine surface, usually a granite surface that has been machined perfectly flat! Then you measure with the correct tool to this plate and see how far off you are in the X and Y directly. Depending upon the machine, aligning the spindle is not easy work and no one answer will work. This could be as simple as loosening the mounting bolts slightly and moving the spindle to align it. Or it could involve using carefully placed shims to align your spindle.

You also have to be careful on some machines as it involves removing other units to get to the one you want to align. Then you have to re-align the units you removed. A mark helps get it back into the general area, but once it has been moved. You will have to re-align everything. One you adjust the spindle, then you need to re-measure and possibly re-align if you haven't done it before. This could easily turn a couple hour job for a technician into a couple day job for you. Once you do it over and over it gets easier. Better to just hire a technician to come in and he should be happy to explain to you what he is doing on your specific machine. You can also watch and learn how it is done. This can easily be money saved compared to a machine cutting out of level for a few days!

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