How do you get the base of a mill square with the vertical column?

I was thinking about all these cheaper bench mills. How do you make them square?
Are they simply machined flat with a face mill/fly cutter? Then just bolted together?
Are they surface ground?
How square are machines made? Like a typical 45 sized bench mill?
How do you measure that 90degree angle to minute accuracy? 90.05, 90.002 degrees etc?
How are larger commercial machines put together? Do they have the base and vertical upright just bolted down?

Shims

A good dti and holder, accurate blocks/ squares for measuring, trigonometry, and shims.
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Apples
The best & correct way is to hand scrape the surfaces, With machine building they machine the face's then hand scrape the surface to get them square to each other, some manufactures grind after machining then hand scrape
There are lots of information on hand scraping here is a video

Hi, I think the term scraping is only the method.....what you use to decide where you scrape is more important.

Scraping one out of true surface to yield another is not a solution.
You need a reference surface to produce one flat surface and then scrape the other one to it.
The base top surface is the first one to get flat, then you make the column bottom face true to it, but also making sure the column is sticking up at 90 degrees to the base surface, so it's a two handed approach.
You will need a square to determine the 90 degrees, and a reference square, long enough to test the column and calibrated and certificated would cost more than the average hobby mill by itself.
In circumstances like this where you just must have a reference square and nothing else will do, you can get away with a simple column type, and that is completely within the ability of the average turner to make one that is dead accurate.
The height of the square is the deciding factor, and with a mill column of 1 metre height you would need a square at least 2/3 rds this length, or 600mm long with a base diam of at least 100mm.
We are talking about an accuracy of 90 degrees +- 00000.
To make one you need a bar of steel 75mm diam and 600mm long, or a piece of heavy wall steel tubing of the same.
With the solid steel bar, the ends are centred and the OD is turned and preferably ground PARALLEL, and one end faced flat with the centre of the bar undercut to leave a land about 10mm wide.....the top face is of no consequence.
Once the bar has been centred ACCURATELY in both ends, the bar can be tested for straightness, and cold rolled or bright mild steel is pretty smooth and may not need turning or grinding if it's acceptable.
This requires a knowledge of lathe work where a steady is set up and the ability to use it.
Once the OD is turned or ground PARALLEL the facing of the end will render it dead square.
There is a cut off point in the dimensions, and I think it would be within the capability of anyone with a lathe to have a 600mm X 75mm square as opposed to going to 1 metre long X 125mm diam, weighing a ton.
If you go to thick wall tubing (which is preferable due to the weight factor and cost) you will need to weld in a bung at the top and the bottom to enable centres for the turning and grinding......thick wall tubing is not very round or smooth on the outside.
Whichever method you use, once made it will be the most accurate reference tool in the shop.
Ian.

This is the generally accepted way to fit up a quality machine. However I suspect most of these low end machines don't bother with a proper fit up and resort to machined surfaces and the precision of the mill to get good enough.

Apples
The best & correct way is to hand scrape the surfaces, With machine building they machine the face's then hand scrape the surface to get them square to each other, some manufactures grind after machining then hand scrape
There are lots of information on hand scraping here is a video

The biggest problem with hand scraping, to improve fit up of a low end machine in the home shop, is coming up with all the tools and instruments to do the job correctly. That is the straight edges, squares and scraping tools to start from the bottom up to get everything right. Squaring up a column isn't really all that difficult but shouldn't be attempted until the two surfaces to be squared have had all the corrections applied if needed.

Hi, I've seen a method where the surfaces were "jacked" out with screws to get the "lean" in the right direction, works the same as sticking shims between the faces.....all roads lead to Rome...LOL.
BTW, if the column of a vertical mill was out by 1 degree to the Y axis, the only effect it would have would be when you drill a deep hole and get the hole out of square to the top face of the job.......most people won't be able to detect an out of square hole.
If the column is out of square to the X axis all that would happen, apart from the drilled holes being out of square to the top face of the job, would be that a facing cutter cuts on the back of the cutter as it leaves the job either way, but provided you completely run the cutter off the job you can work with it.
If you accept the out of squareness your jobs will not be classed as anything near precision for a customer.
For the majority of jobs where end mills are used the out of squareness will not show up on a job or be detectable.
In many cases where a job is held in a vice, the vice jaws are out more than the column and placing a job down on parallels that are on the vice base does not guarantee the job is true either.
I saw a chap attempt to square the head of a Bridgeport mill to the table and got different readings due to the knee being slack to the column.
Ian.

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