What's causing this?

[dhunt]

We have to cut something like 100-200 of these little box things
-they're about 4 x 6 ins. in size.. out of 1.75 ins. thick Mahogany.
We're using a 0.5 in. spiral upcut bit by Amana.


I'm getting this annoying little groove happening in all six passes
(see attached pics below)

The flaw is happening on only one 6 in. side of the boxes, as the machine cuts in Y
going out from my nearby side of the table --but not on the other side, coming back in.

I've had a look at the racks/pinions,gear cogs
and even cleaned the center grooves of the wheels -the rails seem OK if a little worn.

I've cut several of these boxes across the table in several different X-positions
so I feel it's something going on in Y?

_______________________________
Could it be a Z problem?
Could it be a slightly-loose router in the frame?
One of our two hose clamps securing the variable-speed 3.5 hp Porter-Cable is ..ah... in need of replacement
but why is it happening in just this one spot, on one side only?


I've lined up a few of the boxes but, as you can see,
it's not happening in precisely the same place along that 6 inch run in Y.

What gives? Ideas?

[steve_g]

Were these all cut from the same file? It looks like a dwell mark from the bit plunging and retreating. Try using a lead in and out. However, if they are cut from the same file that would not explain the changing position of the marks.

Steve

[dhunt]

Were these all cut from the same file?
It looks like a dwell mark from the bit plunging and retreating.
Try using a lead in and out.
However, if they are cut from the same file
that would not explain the changing position of the marks.

All cut from the same file!
I know what you mean about a dwell-mark, but no it's not that..

The bit does not plunge at that point -it does that clear across the other side of the box!

[Rob Gunn]

Looks like a hesitation in your program that may be caused buy a communication hesitation between your computer and the Machine? I have seen other CNC machines do this. Can you physically see the ShopBot stop, jump, hesitate, jerk... ? Maybe slow the feed way down on a practice part and see if you can eyeball the issue. I may be off base but take a look and good luck.

[Brady Watson]

It looks like that is where the start/end point is.

Select the part in software and go into Node editing - Is there a node there? Does it need to be there?

-B

[dhunt]

Looks like a hesitation in your program that may be caused buy a communication hesitation
between your computer and the Machine?
I have seen other CNC machines do this.

Can you physically see the ShopBot stop, jump, hesitate, jerk... ? ===> No.
Maybe slow the feed way down on a practice part
and see if you can eyeball the issue.

OK -thanks for the suggestions...

Cutting speed is presently 1.3 ins. per sec.
Couldn't hurt to slow that down to 1 in. per sec. or less..
but maybe too I should also FE the cut file and see if there's a built-in hesitation, for whatever reason.

A bit later...
OK I have now FE'd the cut file and identified the lines of code that cut this particular dimension.
I see nothing amiss
so I'm still thinking there's a physical bump or lump or gouge somewhere that's causing this.

[dlcw]

David,

I could also be the natural flex in the machine.

I know when I cut thick blocks, I first do a climb cut all the way around about 1/32" from my wanted cut line leaving a 1/16" skin. I then do a conventional cut on the wanted cut line and I don't have these marks.

[dhunt]

It looks like that is where the start/end point is.

Select the part in software and go into Node editing
- Is there a node there? Does it need to be there?

The starting and end-point for the cut file is shown in the attached photo below
where you see the white pen at lower right.

The flaw is happening at upper left
-the dark pencil is pointing to the area where the flaw is occurring.



Nodes: Our Vector-9 software doesn't seem to have anything like Nodes anywhere in it.

I did as you suggested, selected the part (shows red in V-9)
and then had a good look thru all the possible options under File, Edit, Change, Draw, Axis, etc.
but no Nodes of any sort....not in Vector-9

[ken_rychlik]

You can ramp the down move in and that will help there, but it will still pull straight up when it's done cutting.

I have had to program a tail in some pieces and make the start point on the end of the tail.

There is also a lead in, lead out option on most of the vetric software.

I'm surprised you are able to hold those thick pieces in place with that large upcut bit pulling on em.

Wow, what is vector 9 ?

If your start point is where the white pen is, and you are ramping in, maybe that is the end of the ramp where it pulls up??

[dhunt]

I'm surprised you are able to hold those thick pieces in place with that large upcut bit pulling on em.

Wow, what is vector 9 ?

Clamps may be primitive, but they work!

God bless 'em --I've been clamping now for ten years.
Yes, we have a big old fancy suck-down thang behind the wall thar
we use it mainly when cutting fascia boards outa whole sheets of ply
but for smaller stuff, it's clamps and maybe a few judiciously placed hold-down screws.
Call it life in the islands?


_________________________________
What is Vector-9 you ask.

It's slow plodding Dutch software from ten years ago!
(-and IMServe doesn't respond to their emails! )

Ask the older guys on the Forum...guys who bought Bots 10-15 yrs. ago
when said Bots came with.......Vector-9!

PartWizard and PartWorks weren't even born then!

It's what we know, and it's very sure.
I have oodles of control over making toolpaths and cut files