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CNC problems with PLASTIC



KHK
04-15-2012, 01:53 PM
I have a handle that i want to fab out of plastic. As normial I have one piece of plastic so I decided to do a trial cut in scrap pine wood.

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Everything worked out really good. I was not suprised because I had cut some Oak before.

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This is when the project went down the drain. During the cut the router bit cut some unwanted cuts. This happened when I was not looking, so I reset everying and tried again. Everything was working great and then when I looked away it messed up again. Another reset!! Fineally I saw what happened. The Z axis did not pull completly off of the plastic, and the X,Y continued to do there thing. This caused the gouging into the plastic.

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After much thought I determined that this was not an operator error but a CNC design error. The plastic comes off of the cutter warm/hot and it is at times sticky. The sticky plastic is stalling the Z axis motor. The Z axis motor is 1/10 the size of the X,Y axis motors. The X,Y has built in feed back and if the motor is stalled, it shuts down. The Y axis has no such protection.

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The solution is to increase the size of the Z axis motor and controller. I have ordered a new motor and controller. The new motor is not the same size as the X,Y setup but it is 4 times the size of the existing Z axis motor and the combo has stall protection. The other design problem is the Z axis travel, it is only 1.5 in, this works just fine on plasma, wood, plastic, Al but it is harder to set up. I am looking at changing the Z axis travel as well.

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Gadget
04-15-2012, 02:13 PM
I clamp plastic in a tub and put enough water in the tub to cover the plastic when I cut it on the CNC table Keith. No heat buildup that way.

acourtjester
04-15-2012, 02:34 PM
What a slick idea, you da man Gadget
I hope my haft-himmers don't get in the way when I need to do plastic.

KHK
04-30-2012, 11:26 AM
That may work Gadget, but the real problem is poor design of the Z axis.
New Z design gives me 3.5 in of travel compaired to the old one of 1.5 in of travel.

Z in normal state
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Z in extended state
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As you can see there is a big difference beyween the current motor(left) and the new motor(right). The origional design was for a PLASMA CNC. The CNC ROUTER was an after thought. The origional design works great on CNC plasma.
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Gadget
04-30-2012, 12:52 PM
Keith, I have about 5" of Z travel on my table and am using the 305in steppers. Your new one should be much better.

KHK
06-15-2012, 05:37 PM
The screw shaft for the new Z axis was 1 in to long. The screw shaft is hardened steel. There may be an easier way to cut it off, but I chose the best with available tools. A lathe and a tool post grinder.
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The completed job took about an hour.

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Gadget
06-15-2012, 06:18 PM
Great way to cut the shaft Keith. I should have ground the diameter down on mine when I had to reduce them, it would have turned out better.

KHK
08-03-2012, 05:03 PM
There are two problems with the current design. 1) The height of the unit is too high, making a problem when it is on the wall. 2) All of the weight is over hung, making the bearings life deminished. I have moved the motor to the rear of the assembly. I loose the direct drive and will use a belt drive. There are a lot of trade offs.

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The solid piece of AL was quite expensive. The trial cut was out of wood.

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I used the current CNC machine to do the trial cut and the AL cut. This was quite a chalenge due to the limitations of the current Z axis. I could not find a cheap end mill that would fit in the router so I used a router bit. The bit worked good accept for chip removal which was not good

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KHK
08-03-2012, 05:11 PM
http://youtu.be/TB0zwgPHCUU

Bearing housing after the CNC process
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I made a bearing retainer for the top of the bearing. Not shown
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Gadget
08-03-2012, 07:48 PM
Nice looking cuts Keith, your table must be smooth as silk on the movement. I'll bet you had some of that AL you gave me for that project.

undercut
08-03-2012, 08:08 PM
Man O man is that ever slick! That bearing looks like it fit absolutely perfectly.

WookieWelding
08-04-2012, 10:06 AM
what size end mill do you need ? i have a bunch we toss them at work after a production run ..they are still good for what you are doing

KHK
08-04-2012, 10:30 AM
The end mill that I needed was 1/4 shank 1/4 cutter lenght and 1/4 shank 3/8 cutter both with with 1 1/4 cutter lenght. The end mills that I have are 3/8 shank and above. The Drenel that I use, has a 1/4 chuck.

WookieWelding
08-04-2012, 10:38 AM
The end mill that I needed was 1/4 shank 1/4 cutter lenght and 1/4 shank 3/8 cutter both with with 1 1/4 cutter lenght. The end mills that I have are 3/8 shank and above. The Drenel that I use, has a 1/4 chuck.
you could grind the shank to 1/4 in your lathe for the 3/8th end mill since you have a tool post grinder. i can mail you a 1/4 inch end mill will have to look in my box at work to see how many i have sitting in the bottom of it they are mostly all carbide

KHK
08-06-2012, 05:42 PM
WookieWelding;

Sounds good I will send you a PM.

KHK
08-06-2012, 06:13 PM
This happened about a month ago.
I decided to test the motor and driver, and found that there wes a compatability problem between the CNC controler and the motor driver. I could not get the motor controler to respond to a computer command. To make a looong story short. The controler was made for Orential market, once I had a Orential drawing the problem became clear. I had to design and make a interface board.

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Once the board was completed the testing began.

At first the motor would not make the assembly move:doh2 But it took a tweak of the motor driver current and it took off
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I ran it for about 1,000 cycles and all workrd great!
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Gadget
08-06-2012, 07:34 PM
Nice work Keith, that's way beyond my skill level.

undercut
08-06-2012, 09:39 PM
This happened about a month ago.
I decided to test the motor and driver, and found that there wes a compatability problem between the CNC controler and the motor driver. I could not get the motor controler to respond to a computer command. To make a looong story short. The controler was made for Orential market, once I had a Orential drawing the problem became clear. I had to design and make a interface board.

Once the board was completed the testing began.

At first the motor would not make the assembly move:doh2 But it took a tweak of the motor driver current and it took off
I ran it for about 1,000 cycles and all workrd great!


I'm impressed too. Didn't realize you had such expertise in electronics, Keith. Must come in very handy. Cheers.

KHK
08-10-2012, 10:08 PM
All parts complete, time to install the new Z axis.

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acourtjester
08-11-2012, 02:13 PM
Very nice work it's great to see how others work out the details of their projects. This is a help to other whom are thinking about building a CNC table.
Many different approaches and how they went together to solve the task of moving the torch up/down.
have fun
Tom

KHK
08-13-2012, 11:16 PM
I installed the motor controller in control box.
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The rest was mechanical instalation
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Installing limit switches.
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I had to make new part holder and then time to cut!!:bounce
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Slight tap with hammer and the parts fell out. Slag was holding them in place!
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Project Complete:clap:clap:clap Now I have about 7 items on the honeydo list. Then back to the spot welder project

undercut
08-14-2012, 12:18 AM
Absolutely magnificent! The build is super clean and tidy. Man, I'd have a difficult time thinking this wasn't a production machine! Excellent work!

Gadget
08-14-2012, 06:41 AM
That control box is very well laid out Keith. The mechanical components look factory made. Excellent work.

acourtjester
08-14-2012, 09:15 AM
Funny but I bet sparks turned into big smiles, nice work.

KHK
08-14-2012, 09:27 AM
Thank's for the kind words!