Pen Tester

[kolias]

Has anyone used a home made pen / pencil / marker tester to test for the 1st time a cnc router machine?

As you can see in the attached pic, mine is accurate for a simple square but not for anything more complex.

Since I'm new to cnc and this is my 1st machine, I would like to try it first with a pen on a piece of paper and then use the router.

Perhaps a purchased one but not too expensive?
Nicolas

[Al_The_Man]

I made one up some years ago, I used a miniature linear slide that I got as a sample from a bearing manuf. clamped to the Z axis.
I have used the industry standard 'rosette' pattern to check the tuning as it shows up servo error and or backlash.
http://www.cnczone.com/forums/showthread.php?t=57695
Al.

[CarveOne]

This Solsylva page shows some ways to make a pen holder. A round BIC ballpoint pen can be mounted in a tube with a small spring at the top end to keep tension on the pen so that it doesn't skip or dig into the paper.

CarveOne

[kolias]

Originally Posted by CarveOne This Solsylva page shows some ways to make a pen holder. A round BIC ballpoint pen can be mounted in a tube with a small spring at the top end to keep tension on the pen so that it doesn't skip or dig into the paper. CarveOne

Great ideas CarveOne, Thanks

Also thank you Al for the nice patterns, great way to practice
Nicolas

[CarveOne]

Originally Posted by kolias Great ideas CarveOne, Thanks Also thank you Al for the nice patterns, great way to practice Nicolas

Pen holders are useful for checking gcode without the dust, but drawing with a pen will not show you what happens when the cutter has cutting loads on it. What looks accurate on paper may not be so on wood if your machine has flexing and backlash issues.

The spring from a retractable ballpoint pen is enough tension to use in the tube pen holder idea. The tube needs to be a close slip fit to the BIC ballpoint body and the pen body should not protrude more than about an inch from the tube so the plastic pen body doesn't wobble around. Just run the Z axis down to preload the spring a little and start drawing away.
K&S brass tubing from a hobby shop should have a size that is just about perfect.

CarveOne

[kolias]

Excellent info CarveOne

Thanks for taking the time to inform me
Nicolas

[CarveOne]

I found a piece of brass tubing that is a slip fit to a round pencil but I don't have a tube for the BIC pen available, so I made this one with the pencil just as an example.

Drill a hole in the BIC pen's body but don't drill into the ink tube inside. Screw a short 2-56 or 4-40 screw into the hole to thread the hole.

Using a Dremel tool with a cut-off wheel, cut a slot into the brass tube that is just wide enough for the screw to slide in the slot without hanging up.

The tube for the pen needs to have about the same length relations as the pencil version seen in the photos. You need to glue a short piece of hardwood dowel into the top of the tube. Drop in the ball point spring, then slide the pen into the tube and align the slot with the hole on the pen, then install the screw. When you press the pen onto a drawing surface the pen should easily slide up and down within the length of the slot.

Now you can mount this tube assembly to your Z axis in whichever way is convenient. This pencil version took all of twenty minutes to find the parts and assemble it. The spring even compensates for wear of the point, but you may have to disassemble it to sharpen the point.

CarveOne

[kolias]

Thank you CarveOne, very smart and I will give it a try

Dont have a round pencil like that but I will get some. No problem for the tube

Much appreciated
Nicolas

[CarveOne]

Originally Posted by kolias Thank you CarveOne, very smart and I will give it a try Dont have a round pencil like that but I will get some. No problem for the tube Much appreciated Nicolas

Thanks Nicolas. When you mount this, do it in a way that does not compress the tube or it will bind inside. A very small amount of glue on the tip of the screw threads should be able to lock the screw into the pencil but don't let it squeeze out and glue the pencil into the tube.

I think the BIC pen version will work best. It can even be cut down in length if needed. (might get messy) Just put the pen's end plug back into it so that the spring has something to push against.

How well this idea works depends on how close the tube fits onto the pen or pencil. If you are looking to measure plot accuracy, the pen or pencil can be glued inside the tube.

CarveOne

[kolias]

Sounds good

Hopefully I will give it a try today

Nicolas

[CarveOne]

Very good. Post a photo and the test results if you don't mind. Good or bad. My machines are not working so I can't check my sample yet.

CarveOne

[kolias]

Originally Posted by CarveOne Very good. Post a photo and the test results if you don't mind. Good or bad. My machines are not working so I can't check my sample yet. CarveOne

Here it is CarveOne, your ideas were excellent and the results fantastic.

Had to do some changes / additions and still there is room for improvement but works really good. About 2 hrs work

Was disappointing not been able to use the 1/4" steel rod because the router shaft turns. Perhaps there is a way to keep the shaft locked but right now I dont know about it and used a clamp.
Nicolas