twforeman's Shapeoko 3 #0004 Upgrades - Long

twforeman
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Mon Feb 08, 2016 4:15 am

After dinner I ran the Diamond-Circle-Square test and the results were pretty darned good. I need to run some calibration cuts to tweak the steps per mm settings, but it's pretty close now.

Image

The square was supposed to be 3.500" and it came out 3.508" on the X axis and 3.511" on the Y axis.

The diamond came out 2.264" one direction and 2.260" the other.

The circle was pretty round too.

I ran a pretty agressive feed and speed - .100" passes and 80 inches per minute, and my 1/4" router bit was dirty and may be dull.

But I'll take these results!

I'm pretty happy with the results of my upgrades at this point! :D

Here is a boring video that I shot of the Diamond-Circle-Square test. Looks like I could use some tool path optimization in a couple of places. :)

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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Sat Feb 13, 2016 4:22 am

Another short update with no photos.

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.

Tonight I decided to go down and play around to see if that would be the correct height.

Then 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. :lol:

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!

Perfecto!

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"...

Hmmm... Anyone think that's a bad idea?
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LTEPM
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by LTEPM » Sat Feb 13, 2016 5:15 am

I'd recommend placing one of the end plates with the flange facing out to give you more working width between end plate risers.

I have tiled jobs on 20"X 60" material on the stock configuration. If your risers can be milled parallel to X axis to use as a fence, bonus.

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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by Atonwa » Sat Feb 13, 2016 5:21 am

twforeman wrote: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"...

Hmmm... Anyone think that's a bad idea?
I thought about that when I first saw those risers. Until Carbide3D finally lets us order extrusion by itself we have no way other than the feed through in that direction to handle larger stock. I use the feed through a lot but I guess it depends on what you plan to run.

You could always start with the MDF ones on the corners and if there's an issue go to solid aluminum riser blocks. The bent steel frame should be fine at this width of machine.
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Sun Feb 14, 2016 3:10 am

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/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!

Image

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.)

Image

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.

Image

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.
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by Atonwa » Sun Feb 14, 2016 12:35 pm

Have to say it again, great write up and pictures. I was wondering exactly the most accurate way to set up the steps/mm adjustment to tighten up my machine and this shows it clearly. Learned a lot in this thread.

Since you have a dial indicator handy and did the washer wheel fix could you measure the amount of deflection of the Z axis at the endmill you get now with that fixed? I'm interested and others probably would like a real number to shoot for too.

Also, do you still plan on installing a wasteboard on your t-slot bed and then facing it off to ensure your as level as possible or does this alignment allow you to just throw down a piece of MDF and run? Right now I haven't done this fine of alignment and just flattened an MDF sacrificial board to know I was level with the machine.
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twforeman
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Sun Feb 14, 2016 4:25 pm

I'm not sure how to measure the deflection in a meaningful way since the deflection depends on a few variables like how low the Z carriage is and how much force you apply to the end mill.

I might have to use my trigger pull gauge (really a fancy fish scale) and test it anyway. You know, for science.

As for the bed, I'm going to run the test indicator over it to see how flat and level it is. I'm hoping that it's good enough to use as is.

In any case much of my work is done on fixtures that I flatten.

I'm glad that you are getting useful information out of this thread.

Sent using tapatalk.
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Sun Feb 14, 2016 10:36 pm

Lots of stuff today. Mostly testing and such.

First thing I did was setup the dial indicator to measure the Z flex. I set it up and measured in the X and Y axis with the Z fully retracted and then fully extended.

I wish I had measured it before I made the upgrades so I had a comparison, but oh well. Maybe someone reading this who has a stock S3 can duplicate my measurements.

I ran these tests with the machine on and the motors energized so they would hold position.

In any case, here is checking the in the Y direction at full Z extension.

Image

Here I am checking in the X direction at full Z retraction.

Image

I used my trigger pull gauge to get as close to 10 lbs of force as I could. The gauge only goes to 12 lbs, so I figured 10 lbs was a reasonable number.

In the Y direction at full Z retraction I saw a deflection of 0.025". In the Y direction at full Z extension I saw a deflection of 0.040". Which seems like a lot to me.

In the X direction I saw the same deflection of 0.015" both at full Z retraction and extension.

So it seems to me that there is a lot of flex in the Z carriage still. I can think of several things that could be done to stiffen it further.

I also checked the table for flatness. It's actually pretty good - within about 0.005" most places. But I discovered that the front was higher than the back so I double checked the rail heights and discovered that the back right corner was low so I shimmed it up another 0.010" which makes the table flat enough for my purposes so far.

Image

Then to get some real-world numbers I ran the Diamond-Circle-Square test again and I'm very happy with the results!

Image

The square should measure 3.500" and it measures 3.502" in the X and 3.504" in the Y.

The diamond should measure 2.250" and it measures 2.255" across the flats in both directions.

The circle should also measure 2.250" and it measures between 2.252" and 2.254" all around. So it's even pretty darned round. :D

I am about 99.9% satisfied with these numbers. I could spend a lot more time fiddling around to get a very minor improvement, but I'm just going to go with this for now.

I have to go make dinner now, but after dinner I will make another post talking about some more tests I did this afternoon.
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by GoSpeedRacer » Mon Feb 15, 2016 12:32 am

Silly question but from my time spent on another machine I am curious....

Every time I install a fresh bit (I use 3/32 end mills more or less) I have to cut a hole, measure it, and adjust my bit diameter in Cut2d. I store that as my current bit and whenever I change bits I have to re calibrate. When you are making your cuts and recording your measurements, how do you make 100% certain that the bit isn't part of the skewed numbers? When you do your test pattern for example, if you replace the bit would you see your measurements change like mine?

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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Mon Feb 15, 2016 12:38 am

GoSpeedRacer wrote:Silly question but from my time spent on another machine I am curious....

Every time I install a fresh bit (I use 3/32 end mills more or less) I have to cut a hole, measure it, and adjust my bit diameter in Cut2d. I store that as my current bit and whenever I change bits I have to re calibrate. When you are making your cuts and recording your measurements, how do you make 100% certain that the bit isn't part of the skewed numbers? When you do your test pattern for example, if you replace the bit would you see your measurements change like mine?
That's a good question. I actually measured the bit that I was using and it's 0.250" on the nose.

Cutting a test hole measures both the bit and the calibration of the machine. My goal is to calibrate the machine so that all I need to do is measure the bit.

Professional CNC machines have something called "cutter compensation" where they can change the tool path based on the difference between the bit size that was programmed and the actual bit size. Grbl doesn't have enough memory to allow this right now, but I hope it's on the list for later versions.
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