Level the Table Top

Before doing any testing, I need to level the table top of the machine.  This is done by using a dial indicator and checking each corner.

Each corner can easily be brought into .001 of each outer by loostening the bolts holding the corner in place and making small adjustments up or down.

Test 1, Slow Test

In this test I run a drawing at 50IPM. The results will be used as a future reference for design changes and tuning.  It is also used with the next test to check for repeatability.

I did find some small anomalies in this test and will be looking closer at the next couple tests.

 

Test 2, Repeatability

In this test I run the exact same test on top of the previous test.  This will show the repeatability of the machine.

In this case it looked really good.  Even the anomalies I noticed are repeated exactly.

 

Test 3, High Speed Test

In this test I run the machine at 200IPM to make a new drawing.  This is used to compare against the original slow test to see if any of the anomalies are exaggerated.

And in this case they are.

 

Results

If you look close at the rear wheel, you can see that it is slightly out of round.

 

Here running faster the rear wheel is even more regular.

These problems as well as some of the other jiggles are caused by the machine and gantry wiggling as it changes direction. 

The fist culprite is the casters. While they are designed to fully transfer the bottom of the frame to the floor once the foot is lowered, the actual foot is made from rubber.  These tend to wiggle as the machine is in motion.

 

 

For now I just removed the casters, and will eventually replace the rubber foot with something else.

The next culprit is the bearing trucks.  This is the first time I have used these fully supported rails, but have figured out the purpose of the two grub screws.

The side screw is used to tighten the side to side movement of the truck on the rail.

The top screw is used to tighten the up and down movements of the truck on the rail.

The screws need to be accessible after assembly as they are installed just a little loose and the plates added.  Once all the plates are secured to the trucks, the screws are used to tighten the complete assembly on the rail.

This is a little more complicated fix. Currently the gantry riser sits over the truck/plate assembly. I am going to have to enlarge the plate and move the riser to the outside.  I will add access holes to the screws which will remain exposed.

In addition I am going to move the two trucks to the outside edges, thus adding more stability.  I will lose about 2" of travel by doing this.

 

Other Possible Problems

The belts I am using may be adding some wiggle as well.  It is hard to tell at this point. Once the new carriage plates have been added I can test the belts.  If they do pose a problem, I convert the machine to R&P.

Currently I am also using some Corian (Plastic) as some of the plates.  These are not as rigid as the aluminum that I will eventually be using.

 

On closing

I always do a drawing test on new CNC designs.  They can also be very helpful trouble shooting tuning problems.