[FoxCNC1]

Can you give and example why you switch ? I am intrigued.

[Gilrock]

I'd like to suggest that you quit looking at exact stop mode and CV settings as the source of your accuracy issues. I say that because I went down that rabbit hole last week. You read about all my troubles here and see how I was thinking these exact same thoughts.
http://www.cnczone.com/forums/aspire...s_3d_work.html

If you want to settle it just do a slow speed cut in exact stop mode and see if what you don't like disappears. In my case it didn't. You have the same motors I do so I can tell you that CV mode still gives pretty darn good corners at 100 IPM. The configuration file from CNCRouterParts has the X and Y motors defaulted to 600 IPM max but the Z is set to 100 IPM so that's what I run at when doing 3D work. For 2D cuts you could probably crank it up. Also your speeds are going to depend on how much material you try to cut per pass. I see a lot of people talking about how fast they move their machine but they don't say how deep they are cutting at those speeds. For my roughing cuts I didn't like how the wood was starting to shear in front of the cut if I went 0.25" deep so I changed my roughing passes to 0.125". I set them for 60 IPM and if the cut is going easy I manually increase the feed rate during the run. I could run a lot faster but I'm probably just more conservative since I'm just starting. I didn't like how the machine seemed to make a hard snap when switching directions.

[BuckNaked31]

Sure. Neck pockets. The CV setting will make the corners of strat pockets asymetrical. I want the speed however that CV provides, even though the accuracy is not there. On the finishing pass, I want as much accuracy as my machine can provide, and since it's only the finishing pass, I only have to tolerate the jerky motion for one pass at full depth taking off the last .020"... Another benefit is that by only doing exact stop on the finishing pass is that it minimizes the tool from getting buried in the corners when you encounter anything close to a right angle. The setting to stop CV on corners works for right angles, but a bolt on guitar neck pocket doesn't have any right angles. Don't fear exact stop mode. If you use it correctly, it can work great. I certainly wouldn't use it for anything with a lot of arcs in it.

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[FoxCNC1]

thank you both for the replies. I am going to work on my spoil board and table; basically go over the entire machine and try again.
but it seems most of my problem was the gantry carrier being loose.

[diyengineer]

Probably wouldn't hurt buying a precision square and dial indicator. Have you trammed the spindle? Have you verified with an indicator 3/4" of travel? Usually the steps always need to slightly be adjusted, get as close as possible so over distance is more accurate.

[FoxCNC1]

I have a square, not sure about "precision square" but it's square. I also have a smaller one that I bought from micromark and while back. I did buy a dial indicator, but not sure how to use it beyond measuring runout. Let's say there is some, then what happens after I get that measurement..

But right now I just installed a proper top and spoiled board. So I should look into what you suggested. Also how can I verify the 3/4 of travel?

I would say that after rebuilding the gantry the machine is pretty good, but I would appreciate some more details on what you have bought up, because in all honesty there is always room for improvement.

[FoxCNC1]

But my X axis which is the gantry carrier seems to not be able to cut a straight line unlike the other axis.
There is a slight blow that happens along 6"-8" in the same place.

See below as the wine rack I cut for a friend. Everything looks great except those segments.
I wonder if it has something to do with the steel rails ?

I am thinking of attaching a pencil as if it where a bit and jog up and down the X so really see what is going on.
But I wonder if anyone else has run into this ?

[diyengineer]

Hard to see what's wrong with the picture since it's at angle. How did you go about setting your rails into parallelism?

[diyengineer]

Also do you have one or two steppers driving your gantry?

[FoxCNC1]

yes I have two motors on the gantry (y).

Since I post I decided to wrench on the machine (it seems like a never ending affair with these things...)
anyway, I too a level and squared it against one edge of the table and lowered the spindle down to it. I then manually moved from one end to the next and noticed and it actually separated - meaning my gantry is not squared somewhere, and I did find the spot. Its funny how if you are a tiny fraction of a measurement off, or out of square and then the errors just magnify.

I am going to adjust the gantry tomorrow and I hope that cures the problem.



Gantry support ends :

The far Y side is off by 1mm.

[FoxCNC1]

Hard to see what's wrong with the picture since it's at angle. How did you go about setting your rails into parallelism?

Its really hard to do what you are asking because they have a camber.
and I have no idea where to begin to do so.

[diyengineer]

You need to select one of your rails and designate it as the "master rail". Jog your gantry to your machines putter table limit, Attach a magnetic dial indicator holder to your gantry, and setup the indicators probe on the rails side. Zero the dial. Slowly, 5ipm or so, feed the gantry down the rails and observe the reading. At every point you have a bolt, it's a chance to "adjust" the mis alignment. At first mark your rail every 1" and take a reading at each location. This will be your starting point. Adjust the bowed sections and rerun. If it's to far out, start all over and loosen the bolts to the rail, adjust one at a time all the way down the rail in a straight line. After your master rail is setup, you can do a few things to get your slave rail into alignment with the master. I'd work on your master first just to see what you have.

[diyengineer]

If you have adjustable bearings, another quick trick is to cut a steel or aluminum tube and use it as your standard width between rails. Loosen all rails start in front, shove the rod between rails, tighten bolts, as you move down the table. Quick and easy, and works fairly well if you put some thought into your bar setup.

[FoxCNC1]

The "pro" vcon steel rails are just bowed out like crazy.
I spend about 3-4 hours since Thursday trying to make the best of it.

I did a test cut today as the gantry would not be able to produce a straight rip cut and after all the invested time it seems much better.

I will try another project as soon as I can gain confidence on the machine again.

This thing is like a race car. Needs wrenching between races.

Is this the case for all cnc machines ?

[ger21]

Is this the case for all cnc machines ?

No, it shouldn't be. But I don't think you've ever had yours setup correctly. Once you do, it should stay that way.

The "pro" vcon steel rails are just bowed out like crazy.

Is the extrusion they're mounted to bowed too? If the extrusion is straight, then I'd guess that one or more of the rail brackets are not mounted correctly?

[diyengineer]

Your machine will only run as well as the proper tools it takes to dial them in. A little investment goes a long way!

[FoxCNC1]

No, it shouldn't be. But I don't think you've ever had yours setup correctly. Once you do, it should stay that way.

There may be some truth to you statement, yes this is the first time REALLY taking the time to build a machine and I have learned a ton and gained much experience in both the operation an assembly. I also want to start all over. But I still think that the issues I had required a level of experience I yet did not have.


Is the extrusion they're mounted to bowed too? If the extrusion is straight, then I'd guess that one or more of the rail brackets are not mounted correctly?

The extrusion is fine. It the steel but I think it worked out. I just make a cut and it seems straight.

Your machine will only run as well as the proper tools it takes to dial them in. A little investment goes a long way!

Tell me about it. What a hard learned lesson. I have invested tons to time the past week, I really hope it works well from now on.

That bit right on that edge from what I can tell all along. Before all this, I would bow in a out about a 1/16". Enough to ruin a work piece and not make a straight line.



Since I am in a very detail oriented mindset about setting this up properly, I noticed that my table is "lower" on one end. I am going to verify it it in fact the table or MDF.
We are talking slight 0.01" off. I say this because when I cut my friends piece, there was some paper like residue on the lower end and some marking of the patterns on the higher side.

Do you guys shims your table and spoil boards?

[diyengineer]

Prof- You use a cutter to "face" your entire spoildboard flat. Make sure you get it bolted down tight, and obviously as flat as you can, but in the end, your going to have to "face" it with a cutter of your choosing to obtain proper flatness.

Checkout little machine shop dot com, along with grizzly tools. both have decent tools you will need like precision levels, squares, straight edges, dial indicators and holders, cutters, etc. Its a black hole, meaning you will never have enough tools/tooling haha. Soon learn though the more you have, the better you can complete or setup your machine. I agree with Ger, i think you have a ways to go ironing the kinks out of your machine. Every machine has its own demons as you will soon learn.

[hanermo]

All cnc machines are not like this.

You are useing a flexible gantry.
You are using a flexible head.
You are using non-rigid materials that are not straight.
You are not using the right measuring equipment (like a dti and a proper machinists straightedge or ground reference surface).

When you change 1-4. you start getting better results.
You will also see everything get a lot heavier, and a lot more expensive.

And a LOT easier.

[FoxCNC1]

thank you.