Dimensions off between file and actual cuts

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iampapabear
Posts: 36
Joined: Mon Nov 28, 2011 2:12 am

Dimensions off between file and actual cuts

Post by iampapabear »

Hello everyone,

I have just tried cutting the Paradise Box from Vectric's monthly projects. :D

I have a strange problem. After checking the tool paths in Aspire, saving them with tools selected from my tool database that are the same dimensions as those listed in the file, and cutting them, I find that the box will definitely not go together properly. :o

The pockets in the side panels are only 0.67 wide, though the dimensions in the file, are 0.7656 wide. The bottoms of the pockets are strangely machined. It appears as 3 steps or terraces, one high, one low, and one between them in the middle. I measured them with a digital caliper and there was about a 0.03 difference from highest to lowest. Didn't write it down before I leveled it with an old fashioned router plane.

The front and back panels are also short in their height, the file shows 4.375, the actual cut was 4.15, a difference of 0.225, nearly a quarter inch short.

The bottom is too narrow, as well, cut at 6.0625, but measured in file as 6.25, 0.18 short of necessary width.

I have taken the time to measure the actual wood as cut and the dimensions from the file. I show them below.

The machine is a Shark Pro Plus HD with Bosch 1617 router, carbide bits from Whiteside, Aspire software. Less than 25 hours on cnc and router. Toolpaths all saved properly for the machine...CNCSHARK-USB - NEW ARCS - (INCH) (*.TAP).

The wood is Maple planed to a thickness measured at 0.75 and sized as recommended in the Paradise Box instructions. (I was surprised to find maple so chippy. much more tear out than I would have thought, even while hand planing a piece). The maple was plain-sawn, NOT quarter or rift.

I would appreciate any input on what might have gone awry..........I sure don't have the answer. :?: :?: :?: Some of the dimensions were correct, some not.
Double checked what the software said it should do according to the file, it just didn't do it!
I went over the machine and found all set-screws tight, no loose connections or fittings. If there had been, the two side panels wouldn't have been identical to each other and the front and back panels wouldn't have been either. The "identicality" (is that even a word?) of two pieces which should be identical tells me that the motors aren't missing steps, either.
The wood didn't move on the table, it was clamped securely.

As a fix for this box I will be gluing pieces onto the short panels to give them the proper length and planing the panels to narrower width to fit the pockets. Easier for me than extending the width of the pockets.

Here are the dimensions.

DIMENSIONS OF PARADISE BOX

AS CUT AS MEASURED
FROM FILES


TOP 7.625 x 11.8125 7.813 x 11.875
Carved area 10.375 x 6.8125 10.375 x 6.25
Border 10.875 x 6.75 10.875 x 6.75


FRONT PANEL 4.15 x 12.09375 4.375 x 12.188

Carved area 2.915 x 10.375 2.875 x 10.375
Border 3.37 x 10.875 3.375 x 10.875


SIDE PANEL 5.43 tall 5.56 tall

Pockets .67 wide .7656
Inside Pocket 3.6 x 6.25 3.6094 x 6.2188
Outside Pocket 4.25 x 7.75 4.375 x 7.75


BOTTOM 6.0625 x 12.125 6.25 x 12.188

I would sure like to hear if anyone else has had similar dimensional differences in projects.

Thanks

iampapabear
Posts: 36
Joined: Mon Nov 28, 2011 2:12 am

Re: Dimensions off between file and actual cuts

Post by iampapabear »

OOPS...

Well, the table of dimensions didn't post well, I have attached it as a text file, should read much easier.

Thanks
Attachments
DIMENSIONS OF PARADISE BOX-differences 2.txt
(557 Bytes) Downloaded 217 times

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wolffie
Posts: 283
Joined: Sat Mar 24, 2012 4:50 pm
Location: Far North Queensland, Australia

Re: Dimensions off between file and actual cuts

Post by wolffie »

Clamp a bit of scrap to the table.
Try loading the file.
Click on Step.
Lower router level with board.
Set XYZ0
Mark where the bit is sitting on the board.
Raise router 1"
Move router 5" to the right.
Lower router level with board.
Mark where the bit is.
Repeat in the other directions.
I can never remember which direction is XYZ :oops:
Check whether it actually has moved 5" or whether it is out.
That is the problem I am having with my HD.
It is not moving the distance it says it is.
Cheers
Wolffie
I am never going to die, I live in Paradise already

drueth
Posts: 208
Joined: Sat Jul 09, 2011 7:09 am

Re: Dimensions off between file and actual cuts

Post by drueth »

Iampapbear

It would be my guess the dia. of your bits are not what you belive them to be, this is a very common problem. I have found it pays to lay out a 1" square and than cut it on a pice of scrap with each different bit you intent to use. Carefully measure the square. If the measurement is under 1" The dia of your bit is less than what it is rated at. So let say the square is only 96/100 of an inch. and you are using a .25" end mill . Go back to Vcarve and edit ( this will only effect this cut file) the dia of the bit to be .23 and try the cut again. Once you have a good cut. You can change the dia of the tool in Vcarve by using select change the value and than apply ( this will change the tool data base) . It also pays to keep a log that records what you find to be the dia or angle for each bit you have. With an end mill I have found they are mostly under sized. With a V bit I have found the angle is less than what it calls for and also the dial is also less than what is calls for. If the dia of a V bit is also off it will not affect your cut much at all.

As far as the steps or terraces I am not sure but one thing that can cause trouble is your speed or depth of cut on each pass. It is best to back off each until you get a better feel for evething.

I hope this help.
drueth
Shark Pro Plus HD
new to CNC 12/2012

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wolffie
Posts: 283
Joined: Sat Mar 24, 2012 4:50 pm
Location: Far North Queensland, Australia

Re: Dimensions off between file and actual cuts

Post by wolffie »

drueth wrote:Iampapbear

It would be my guess the dia. of your bits are not what you belive them to be, this is a very common problem. I have found it pays to lay out a 1" square and than cut it on a pice of scrap with each different bit you intent to use. Carefully measure the square. If the measurement is under 1" The dia of your bit is less than what it is rated at. So let say the square is only 96/100 of an inch. and you are using a .25" end mill . Go back to Vcarve and edit ( this will only effect this cut file) the dia of the bit to be .23 and try the cut again. Once you have a good cut. You can change the dia of the tool in Vcarve by using select change the value and than apply ( this will change the tool data base) . It also pays to keep a log that records what you find to be the dia or angle for each bit you have. With an end mill I have found they are mostly under sized. With a V bit I have found the angle is less than what it calls for and also the dial is also less than what is calls for. If the dia of a V bit is also off it will not affect your cut much at all.

As far as the steps or terraces I am not sure but one thing that can cause trouble is your speed or depth of cut on each pass. It is best to back off each until you get a better feel for evething.

I hope this help.
If the problem was the size of the bit, then the difference would be the same on every cut.
Sometimes papabear's cuts are spot on, sometimes a little bit out and sometimes a lot out.
Something is definitely wrong somewhere.
Cheers
Wolffie
I am never going to die, I live in Paradise already

drueth
Posts: 208
Joined: Sat Jul 09, 2011 7:09 am

Re: Dimensions off between file and actual cuts

Post by drueth »

Wolffie

I don't disagree with you but I would like to try to shout all the ducks befor I go for the bears. Many times I have found bits to be under sized and this will cause a problem. If the cut is to aggressive and the clamps are not holding the board secure it can move and through everthing out. I would very much like for our new friend check his/her bits and and let use know if they are part of the problem. I have read ever one of your post and feel if it could go wrong it all ready has for your machine. I hope you finaly get it to work because I would very mucy like to see what new projects you come up with.
drueth
Shark Pro Plus HD
new to CNC 12/2012

jeb2cav
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Re: Dimensions off between file and actual cuts

Post by jeb2cav »

I think Drueth's ideas are some of the first things to look at. In addition to that, I'd run some tests that enable you to get a better sense of what feeds and speeds you want to use for a given material.

If you were using the default values that Aspire would generate, the feed rate and the depth of cut may not be optimal for your use. You can run some tests using squares for example against scraps. For pockets, the tip I got from a cnc'r at a conference is to cut the pocket down to about 0.03 or so, and then run a separate toolpath on that last bit of the pocket depth. I generally start with a depth of cut of 1/2 the diameter of the bit (and not the full diameter) as well. With regard to speeds - I generally use 75 ipm, and then use the FRO slider in the Control panel - starting at 50 typically and moving up in speed. That way I can use the same tap files against different material - the use of the FRO enables me to adjust the feed rate from the control panel vice having separate tap files with different speeds.

Another good idea I've seen recently is to use a permanent marker after tightening the bit to mark the starting location of the bit in the collet. This would help you identify slipping as well.

The undersizing in my experience is either a bit size not as advertised, or too fast/too deep a cut. Another possibility in this case is that you may have bumped a setting in the project, and instead of cutting in or on or outside the vector, it got changed and you didn't notice it. I haven't tried this project myself, so maybe rambling a little. Intuitively, if you ran the project 'as is', using the default tool database settings, and at an FRO of 100%, you may simply have been trying to carve this too fast and too deep (if not a tool size issue).

You mentioned checking all the mechanicals - I'll assume you also have maintained a good lubrication state, but if you haven't, that can contribute as well.

rungemach
Posts: 460
Joined: Mon Aug 02, 2010 8:24 am
Location: Sarasota, Florida

Re: Dimensions off between file and actual cuts

Post by rungemach »

drueth points out something very valuable here, and not often considered. Thanks.

when you do a 1' square, measure the square you cut out, and also the hole that was left behind.

With that you can verity that the dimension of the centerline of the cuts is accurate in both x and y separately, as well as the effective diameter of the bit, collet, router combination. Bits not being the exact size, sloppy collets, and router runout all add up to the that combined effective size result. Usually a greater diameter than the nominal tool size would be.

if you are consistently "off" by that amount, the problem might be a duck.
if it is way more, its a bear...

4DThinker
Posts: 951
Joined: Wed Jun 27, 2012 9:00 am

Re: Dimensions off between file and actual cuts

Post by 4DThinker »

I ran into some X dimension error today as well. Tried to cut a simple rectangle. Drew a rectangle exactly the size I needed, then created a profile around it. Cut out fine, but when I tried to fit the piece it was about 1/16th too narrow. The Y dimension was spot on. Cut it again and got the same error. Finally drew a new rectangle and added 3/64 to the width an got a piece that fit. Have NO idea what is up here. Used an 1/8" spiral upcut bit that has been perfect up to now. Have the precision collet on my Bosch Colt. The rectangle was 3.78"ish by 3". Had to change it to 3.826875" by 3" to get the 3.78" x 3" rectangle I wanted.

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wolffie
Posts: 283
Joined: Sat Mar 24, 2012 4:50 pm
Location: Far North Queensland, Australia

Re: Dimensions off between file and actual cuts

Post by wolffie »

It does not matter what you do or try it, is a manufacturing error.
When they made the HD they changed the lead screw pitch and somehow it does not agree with the control box software :roll:
I just received a program that was supposed to fix the problem, YEAH RIGHT
Now it is running at double speed and double distance.

It is not me who is jinxed at all.
Draw your own conclusions.

Wolffie
I am never going to die, I live in Paradise already

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