In the final installment on scraping the critical surfaces of the MH28V CNC conversion project mill, we'll be sorting out the entire Z axis - the from the machine base column mounting face to the spindle block swivel lock.
It's been quite a journey, learning to scrape the entire mill over these years. Yes, years. I got very busy with another business along the way, but we're moving along fast now! This time we're focusing on getting the Z axis column ways perfectly straight, squaring those ways up to the rest of the machine, and then making sure the spindle sits parallel with that axis. It's an exciting part of the scraping process because it's a very noticeable part of the machine, both visually and functionally.
Getting the Z axis ways flat and parallel was much the same process as getting any of the other dovetail arrangements on the machine sorted. So, that meant step scraping the flat ways into flatness and parallelism, before finish scraping using a dovetail straight edge. Once those flats are done, you go straight to printing and scraping one dovetail face until it's flat. Now that you've got one flat dovetail face, you can use that as a reference to get the other dovetail face parallel and flat by measuring the distance between with with precision cylinders in them - just another form of step scraping, really. Now you have beautiful, straight dovetail guide ways.
The next logical step is to get the female part matched into your new Z axis dovetails. Again, similar to how we did the X/Y saddle - get the fixed dovetail face matched to the male piece by printing against it and scraping. Squareness of the dovetail faces is of no concern in this case because the spindle head can swivel left-to-right on the MH28V. Once you've got the fixed side sorted, focus on getting the gib matched in without running out of travel (again, plenty of details about this in the previous video.
Now that you can confidently traverse the Z axis with the Z carriage, you can check it for squareness, so we assemble most of the machine, the base, X/Y saddle, table, column, and Z carriage. Place a high precision master square on the machine table and attached an indicator (in our case, a 0.01mm indicator) to the carriage and check the Z squareness in the X and Y directions. From there you scrape the rigid mounting faces between the column and the base until you've got good contact - most particularly on the outer edges - and the Z axis sits acceptably square. Squareness of within 25um over 200mm is pretty good for most applications - which is what the X squareness came to, and the Y squareness come to basically zero - perfect.
Finally it's time to scrape the swiveling interface between the Z carriage and the spindle block so that the spindle sits parallel to the Z axis or square to the table (basically the same meaning if done well). This is how we did it, but ideally, this swiveling interface should also be parallel to the Z axis so the spindle stays square when using the swivel feature. So, to adjust squareness of the spindle, you'd have to readjust the dovetail flats of the Z carriage, but that is a lot more work because you'd have to go back and adjust the dovetail faces too. Modifying the flats always modifies the engagement of the dovetail faces too.
Also, something that wasn't covered in the video is that you need to ensure the column is mounting orientation puts that swiveling interface parallel to the X axis or the spindle will move in the Y axis when swiveling. This alignment is maintained by tapered dowel pins in the column mounting. Again, I'm not planning to use the swivel once the whole machine is converted to 5 axis CNC, so I didn't waste time on it.
If you’re interested in knowing more info about the process than I could pack into a YouTube video, I post extended cut versions of each episode (wherever appropriate or possible) on the Mach Super Patreon page for members, where they can expect their comments to be heard and responded to. Additional perks include getting access to all 3D, CAD and texture files used to make the show.
