I did decide that three layers of 3/4″ MDF was too high for the risers, so I glued up some double-thickness risers a couple of days ago.
Then I decided to go down and play around to see if that would be the correct height.
I realized that in order to replace the risers I would have to remove the rails from the end plates. Again. This is because the bolts are directly under the rails. Sigh.
So I took my Shapeoko apart. Again. I’m beginning to worry that I’m going to wear out the threads in the ends of the rails.
I grabbed the new risers and some scraps of MDF and played with different heights.
- No risers is definitely not high enough.
- A single layer of MDF might work, but I think more height would be better.
- Two layers looked pretty good.
Then it struck me that I had my Shapeoko 1 sitting right there and I was pretty happy with the height on that machine. So I measured it. My S1 has about 4″ of Z travel and about 5-1/2″ of height under the collet.
The Shapeoko 3 has about 4″ of Z travel, and if I put the double-layer risers under the end plates I can get 5-1/2″ of clearance under the collet of the router without hanging the router too far down!
So, double-thickness it is!
Then I had another thought – If I only put supports under the end plates where the rails are and leave the center sections open I could have a 1-1/2″ high pass-through in case I wanted to mill on something longer than about 12″…
The next day I decided to go with just 3″ long blocks for the risers, so I cut 8 pieces of MDF and drilled holes in them.
Then I bolted down the front end plate – squaring it up to the face and re-bolted together the machine. (See earlier post.)
Then I made all four ends of the rails the same height again (see earlier post again.) It went a lot faster this time since I had a good method for doing it. All four corners are within about 0.002″ in height from the table top.
Then it was time to calibrate the steps per mm. The default value (40.020) will get you close, but I changed the belts to 9mm and made them pretty tight and discovered that it was off quite a bit.
The first step is to measure your 1-2-3 blocks. I happen to know that mine are not exactly 3.000″ long, so I measured each one and added all four together to get 11.995″ (three measure 2.999″ and one was 2.998″.)
Next I stacked up my four 1-2-3 blocks end to end with a square clamped to the end for a stop. I bolted this to the table just to keep it from moving.
I attached my test indicator to the machine using the 1/4″ dowel I added to the spindle mount and set it to zero on the end of the stacked up blocks. Next I lifted up an inch to make sure I cleared the bolt, moved down 11.995″ and looked at the indicator. It took me a couple of tries before I realized that it was moving so much too far that it was maxing out the indicator!
Once I figured that out I tried again and told it to only move 11.900. Then I jogged it over 0.010″ at a time until it moved the needle past zero. The programmed travel was 11.965 for an actual movement of 11.995.
So I took the programmed travel and divided it by the actual travel to get the correction factor (0.9975) Then I multiplied the current steps per mm by the correction factor to get the new steps per mm (39.919). I entered this in as $101 and then ran the test again to confirm. It was close, but not quite right, so I ran the correction calculation again and came up with a new steps per mm of 39.902. This time the test was within 0.001″ and I called it good.
Then I rotated the stack of blocks 90 degrees and repeated the process on the X axis. The new steps per mm ended up being 39.905 – pretty close to the Y value (not really a surprise.)
Finally I moved on to the Z. For the Z, since I only have about 4″ of travel, I just stood a 1-2-3 block up on top of another on for a 4″ height. I had to move the test indicator to a 1/4″ dowel fastened into the collet. Then I set the test indicator to zero on the top and moved down 4.000″ The correction was not a much as the X and Y – I assume because the belt is not as tight. The new steps per mm ended up being 40.012.
Tomorrow I’ll run the diamond-circle-square test again – maybe slow the feed down a little. I expect it will come out just about on the money this time. I might make some square pockets too just to see how close they come.
I might also do some speed tests milling holes. I have a job I currently do by hand using Forstner bits on my drill press. It takes about 12 minutes per part to do 50 holes by hand. My Shapeoko 1 was not rigid enough to do that job faster but I suspect the Shapeoko 3 will be.