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martmar
01-30-2009, 11:42 PM
Greetings,

I am running in to a nagging problem with sharp internal corner cuts on my BT48 standard. The machine plunges in the corner making an indention that I can’t seem to prevent from happening. I understand that if the error is consistent then it is probably the design but in this case it can’t be because it is just a simple angle with one node in the corner of the design. I am using a 60 degree v-bit running at 30 ips feed, 15 ips plunge, 13,500 rpm and carpet tape is what I use for hold down. These setting have given me the least amount of chatter of the configurations I have tried, but the my problems have been consistent with all setups. Any thoughts any one, I have attached a picture of my troubles.

Thanks in advance.



3630

dubliner
01-31-2009, 12:07 AM
Hey Marty, that looks like a similar problem I was having. MIne was caused by the Z car rollers being loose or too tight, there are 4 adjustable ones, and it was a combination thereof. Stick your finger inside the z rail & if you can feel the v wheels moving too freely or you can tell they are way too tight,(disengage the z motor & lift car up & down to feel for "just right" ) then use the flat wrench to dial in the eccentric wheels. I still have a little tweaking to do but it improved it to within 5 percent of correct. Hope this helps. Neville

martmar
01-31-2009, 03:19 AM
Hi Neville,

After looking at my cuts that i have made, I see that all of the internal corners do not have this problem it is more on the corners facing the x-axis. If it had something to do with the z-axis this would happen all the time correct. Oh yeah and by the way my speeds in my first post are in IPM not ips sorry.

Gary Campbell
01-31-2009, 09:15 AM
Marty..
What Neville says is correct. You have some movement somewhere in the system. This is usually caused by a loose roller adjustment. The lateral forces on the bit are different when plunging versus moving.

Go thru the adjustment procedure for the Z extrusion rollers, the YZ car rollers and the X movement system. That should solve it.

Another thing that may help is to move the start node to the center of a straight section of the part and ramp the bit in rather than plunging into a corner.
Gary

srwtlc
01-31-2009, 09:26 AM
Marty, if you know that everything is tight with the machine, I'd try a different V-bit and see if you get the same results. If the angle of the bit isn't the same as what is programmed, you can get the results that you're getting. Holddown and improper Z depth setting can cause it too.

srwtlc
01-31-2009, 09:31 AM
Here's more info on v-bit angles. http://www.vectric.com/forum/viewtopic.php?f=3&t=2164

Try the angle test file.

martmar
02-05-2009, 12:18 PM
Thank you to all who posted. I tried to create a bit angle test, actually that is what is in the picture with those results on all my different angles. So, I tried adjusting my buddy and my results have got better but the problem has not totally gone away. I dont know if I am adjusting the x-axis correctly there might be where my problem is. See when moving it in to my home I had to take the table and rails off to make it through my door. Maybe I never got it back aligned. Is there a technique to adjusting the x-axis?

Thanks again guys I appreciate the help.

martmar
02-22-2009, 04:59 PM
Still having the same problem with sharp internal corners. I have adjusted the eccentric bearings as suggested with no acceptable results. When I push on the spindle while cutting it works fine. I am wondering if their could be something else that could be causing the problem that somebody has experienced. I am willing to try anything right about know.

Thanks

Marty

stevem
02-23-2009, 06:38 PM
Marty, when you say that you're pushing on the spindle, are you pushing up, downs or sideways?

The overall cut quality of your part doesn't look very good. It appears as though you have a lot of play in the X and Y axis.

martmar
02-23-2009, 07:07 PM
Hi Steve,

I push sideways. Everything seems real solid when the power is on.

richards
02-24-2009, 09:21 AM
If you're using V-carve pro (or Shopbot equivalent), try redefining the angle of your V-cutter. Back when Bruce and I were working on the FreeDoors program, I found that just because a cutter is advertised as x-degrees doesn't mean that the cutter is actually that size. Thinking back to High School Geometry will remind you how the width and depth of a cut will change based on the included angle of a cutter.

myxpykalix
02-24-2009, 12:12 PM
Have you tried a test on scrap using a different font? It might have something to do with that, as oposed to a physical problem with the bot?

harryball
02-24-2009, 02:29 PM
Marty,

Reviewing the thread I think the issue must be in the Z car somehow. This is based on you saying when you push sideways the cuts are good, when you don't there is a problem. That is a physical problem. Nothing in software or bit geometry should allow your problem to go away completely by applying physical pressure to the cutting head.

I would call Shopbot, refer to this thread so they can see your photos. You will need the flat wrenches to make some adjustments but I agree with Nev, something is loose.

At the moment the problem occurs when X Y and Z are moving at the same time. This creates forces not seen at any other time while cutting 2D. If you can imagine cutting straight force X and Y the Z would stress in such a way as to have constant force on it. When you start moving Z too the force dynamics change and any little slop will show up.

As for pushing and it feeling solid, the amount of variation that could cause the cut quality issue may be imperceivable to the touch.

Don't give up, take a deep breath and think it through and don't be afraid to call shopbot for help. These are solid little machines.

If there is anything I can do, let me know.

/RB

kevin_morin
02-28-2009, 12:20 AM
Marty, we just unpacked a Buddie 48 and had some tolerance issues in our unit.

We finally found the all-thread used to connect the X-table motor mount to the side of the table was too tight. This meant the X drive pinion gear was not fully engaged into the rack on the 48" power stick. The play in table movement only showed up for a few thousandths while the X table reversed direction, similar to the cuts you've shown.

We loosened two nuts on the allthread, making this link just slightly longer allowing the gear to engage deeper into the rack. To make sure the X motor gear moved back to the fully engaged postion each time we used the disengagement handle on the 'front' of the router, we move the spring tension point back away from the motor mount to increase tension and help to insure full engagement by the X motor's pinion into the table's rack gear.

This fully cured our cutting problems and we're cutting the test files with acceptable accuracy and repeatability.

might be worth checking on your machine,

cheers,
Kevin Morin

harryball
04-11-2009, 09:47 AM
Guys,

Marty needs some hands on help with this issue and is becoming more discouraged by the day. I feel almost certain his issue lies in the X axis, not the Z axis. I spoke with him on the phone and he sent me his cut file. I ran it on my bot with the same material and got an almost perfect result. Only a bit of tool marks because I just turned on the vac and cut the small emblem. I spoke to Marty again at length and I believe one of 2 things are happening.

1) The X axis is binding and slightly lifting the table when it changes directions. It wouldn't take much but it would create the results he's seeing.

2) The X axis has some backlash or lost motion causing the X position to be slightly wrong in relation to the Z for a moment during direction changes.

Here are my results for comparison.


3631

This was on a PRT Alpha 96 w/4HP spindle on a 1/4 zone with 2 fiens pulling and that's it. Using a 60 degree .01 engraving bit the results were very acceptable. Marty has a PRS Buddy 48 Standard with the aluminum table and it should be able to be at least as accurate as mine when moving so slow.

I am unable to make the trip to Athens GA which is a little over 2 hours from me. If someone is close by and would be willing to help him out email him and let him know, I'm sure you could get a nice lunch out of it.

/RB

cnc_works
04-11-2009, 11:51 AM
Marty, just as a diagnostic test, have you reversed the path of the cut so it goes clockwise instead of counterclockwise or vice versa? This would change the cutting forces and perhaps give you some additional information if it changes the cut pattern.

Donn

harryball
04-11-2009, 12:54 PM
He has Donn, he said the problem moved to the other side. Since it would be traveling in the opposite direction when it reaches the corners it would seem something is going on with the X.

I've been encouraging Marty to post and talk to you guys, on one hand I think he feels like he is pestering and on the other hand I don't think he knows what to say. He really is focused on making what he wants to make and while his aptitude is not in question and he does great using the machine, it's not "clicking" for him when it comes to the more subtle mechanics of the machine itself.

Marty? Talk to us man!

/RB

Brady Watson
04-11-2009, 01:47 PM
There are really only 2 areas on the X axis that could cause rough movement or binding:

1) The v-rollers attached to the AL table - Dis-engage the X motor. If you have a powerstick handle, just loosen it - if not, Loosen the nut sticking out of the front of the machine apron on the 3X3 Xmember and drop the motor. Test movement of the X axis (the table moving in & out) to see if you get smooth travel when pushing and pulling from the center of the table. If you feel vibration, you may need to 1st clean the rails & rollers, then adjust the eccentric nuts on the v-roller bearings. One side is adjustable, the other is concentric mounted and non-adjustable. Inspect, observe & adjust as needed to achieve smooth movement.

2) X axis pinion to rack mesh & backlash. Engage the X motor into the rack under the AL table. With the X motor UNPLUGGED from the X motor port (channel 1) in the back of the control box, move the tool like you did for checking the bearings - front to back, noting any motor cogging. You will feel a small amount regardless, but you should be able to tell if the motors are meshing correctly. If you are not sure, UNPLUG the Y motor from the control box (channel 2) and move the YZ carriage across the gantry to get a feel for how the movement should be.

You also want to make sure that the pinion gear is correctly meshing with the rack. Make sure it isn't off to one side. Make sure the rack is wet with grease.

Plug the X motor back into the control box & power it up. Grab the table and wiggle & jiggle, listening for any excessive slop/backlash in the X motor to rack. The tesion of the pinion to rack should be neutral - that is to say, you don't want it too loose or too tight. Observe & adjust as necessary until you get it dialed in.

Keep in mind that these tools are pretty simple, and there is little that you could 'screw up' - so be adventurous and dilligent and you will get it dialed in correctly.

-B

harryball
08-26-2009, 09:13 PM
Just an FYI and a chance to refresh this thread. I have Marty's machine in my shop. I have carefully gone over it top to bottom and I've noticed a few minor issues that should not be causing the problem but might contribute.

I do have a couple of questions at this point. His PRS Buddy Standard is the 48x24 with aluminum table / non-powerstick version.

The X motor under the table in engaged with a threaded rod, no spring, no handle and looks somewhat "rigged" he said it came that way... could someone share photos of how their's is setup?

The pinion on the X motor under the table is only about 30% to 40% on the shaft of the motor. It is keyed and seems solid. I would like it to be further engaged but it is currently centered on the rack. Any further onto the shaft and it will not engage properly. Are the others of this style that way or is a bracket installed wrong? pictures if you got em.

/RB

mwpfeifer
08-27-2009, 12:11 AM
Robert,
You have mail.
Hope it helps.
Mike

erik_f
08-27-2009, 11:44 AM
The threaded rod was standard on mine...I had to loosen mine because it was adjusted so tight it was causing the blue cross member that was holding the motor to bow up. Since his machine is in your shop why not try your control box on his machine and see if that changes anything. Also...is he using the same PC to run the control box at your place or are you using a different machine? It looks like it could be a COM issue that I've had in the past when trying to run my standard too fast on 3d files...and this seems to be happening on a 3d move. If you can't swap the control box out with yours why not try swapping out the driver internally in his box...in other words put the x driver on the y and see if the problem follows the driver. I know this can be perplexing, but like Brady said...these aren't that complicated. If you go through each area in question one step at a time eliminating question as you go along until you isolate the real problem.

harryball
08-30-2009, 06:45 PM
Got the mail, thanks!

Erik, it is interesting that your threaded rod was too tight causing the mount to flex. My first inclination is that the X motor is binding or somehow applying lift pressure when it changes directions. I've been busy and was planning on powering it up today, but we have been covered up with thunderstorms all day.

I run a PRT Alpha so I can't swap controllers. I don't beleive the controller is the problem, I'm certain it's mechanical.

/RB

harryball
11-02-2009, 09:23 PM
OK, it's been a while and not because I've been working on it but I've been too busy to work on it. Anyway, I figured it out and "fixed" it.

The problem was a collection of things adding up to large error.

Briefly in the order I found and corrected them:

- The gantry Y car was a little loose. I don't know if that was always the case or it happened during moving but it was corrected.

- The bit geometry was wrong. The 30deg engraving bit is actually 32 to 34deg or some odd such. It was a generic unknown brand. I used an Onsrud 30deg bit for the rest of my testing.

- The bit geometry was defined incorrectly in the cut file. Instead of entering 15 degree for the 30 degree engraving bit it was set to 30 implying a 60deg bit to the software.

- The table was indeed lifting and I almost couldn't figure out why. It had to do with the X mounting bracket underneath. I doubt I can explain this well but... The bracket seemed mounted a little low and there was a notch cut into the bracing bar that reaches front to back to allow the bracket to clear. When the bracket was in place with the rod pulling forward and the back of the plate solid against the brace bar, there was no more adjustment but it was engaged in the rack. The bolt was too small for the hole and as the direction changed even though it was bound the bracket could lift straight up slightly. This allowed the table to lag and lift during direction changes slightly. VERY subtle to find. Corrected by using a larger bolt and slightly enlarging the bolt hole to accommodate.

- Software output of the cut file to 6 decimal places. Going on a tip from the Beta group Vectric guys I dropped the accuracy in the post processor from 6dp to 4dp. There was an improvement so I left it. Don't ask me to explain it. The best I could figure is for a machine with less accuracy rounding became a factor.

All of this solved about 75% of the error.

- Backlash in the motors. While cutting such a small detailed item the backlash in the motors became a factor. Replacing the 24T pinions with 20T pinions solved another 24% of the problem. The last 1% is only apparent because I know exactly where to look and find the error with a loupe. By the naked eye, yeah on some you can spot it but if you didn't know to look you'd never notice it.

While changing to the 20T pinions the Y axis was a quick swap. The X axis required the bracket to be removed and modified somewhat more aggressively. The Z was already 20T.

That's about it.

Results...

Front of test sheet


3632

Back of test sheet


3633

Cut with the unknown bad geometry bit


3634

Cut with the Onsrud bit, same cut file


3635

All fixes applied. I cut 10 of these in a row, quality varied slightly but all were acceptable. The table has not been surfaced recently either.


3636


/RB

Gary Campbell
11-02-2009, 10:17 PM
Robert...
Nice post! I am sure that I am not alone in giving you the well desrved pat on the back for perservering thru all the minutia to find the causes of Marty's problem(s).

Since I have gone thru similar "adventures" in the past, I admire your patience and fortitude. Most of the time there is a mechanical reason for the poor cut quality. It could be worn, loose, misadjusted, poorly designed or improperly installed components. Your solution should be a text on the process of elimination.

Nice catch on the bit geometry errors. Too many are way to willing to accept the defaults in a Cad/Cam application or assume a bit is anywhere near the advertised, especially the lesser expensive varieties.

We all need to remember that there is only ONE component in CNC with any intelligence. That is the operator. He is responsible for all input into the software and toolpath parameters. He is also responsible for maintenence. These machines can cut some pretty awesome stuff if we keep 'em tight.

Again, Great Job!
Gary

GlenP
11-03-2009, 01:34 AM
Hey Robert, your pics of Marty's are exactly what my machine vcarves corners like. Thanks for your emails the other day and shopbot is helping me to try and resolve mine. You told me about some potential loss in move and jog speeds by going to the 20t pinion. Did you have much loss? I have some new pinions on route and hopefully they help with mine. Last week I did a maintenance to all motors and cleaned off old grease and replaced my set screws on the pinions. The ones that came with my machine were not very long and the allen wrench would strip before I could really crank them tight. Once I changed to a longer set screw I had more bulk to hold the wrench and really tighten them up. As of right now I still have to do a finish pass with sharp corners turned off to get somewhat acceptable. Hopefully I can get mine resolved in the coming weeks. Thanks for posting. I am sure Marty will be happy once he gets his buddy home and making some shavings fly. Did you have to change software parameters for the smaller pinions? Sorry if that may seem like a stupid question to some but I am not a programmer or math pro, darn good with wood though.

tmerrill
11-03-2009, 05:37 AM
I worked a little off-line with Robert and discovered my machine was doing something similar. But the problem and solution was different, so I offer it as another possibility for anyone having a cut problem using V bits. It really became apparent when I was trying to complete some inlays using the V-carve method - one side of a component was perfect, the other had a gap.

For me, my router was no longer exactly vertical to the bed. It was only off a small amount, but picture the issue created with a v bit - on one cut side the angle is larger than it should be and on the opposite side it is smaller. Compound this with the fact the router most likely isn't tilted exactly in one simple direction, meaning all in +X, -X, +/- Y, but in a combination of them.

Now with the router vertical again, the quality of the inlays have returned.

Tim

navigator7
11-03-2009, 08:47 AM
I'm surprised not to read any mention of using a dial indicator in this great thread.

You could immediately detect Tim's problem above....and adjust.

Backlash is common on manual lathes and you can "see" the effect on the dial in "thousandths".

Having said that, I see some great work coming from these machines. Problematical errors like Marty's should pop out as a wildly spinning needle or an odd deflection on the dial indicator inconsistent with all the other moves.

I was always impressed that a dial indicator on a heavy lathe, with a heavy four jaw chuck could pick up the smacks of light taps from a lead hammer.....and it provided feedback as I tightened the jaws.

Used properly...a dial indicator with a mag base is a gold mine.

I understand the collect size on these machines are 1/2".
Investing in a 4-6" piece of turned, ground and polished round stock or an actual test bar be acquired and properly protected and stored. The sooner you get these two components the sooner you can make measurements on such things as runout on the spindle bearings, back lash, true square to table and table level.

Recording the spindle reading with a date...might be helpful a year later when the readings have quadrupled and you have measurable noticeable change and documentation.

If you are like me...you write this stuff down like a monkey doing a math problem and carefully file it away never to be found again!
;-)

harryball
11-03-2009, 10:12 AM
Chuck, I did actually use a dial guage and a micrometer during my diagnostics. I'm just giving a 30,000 ft view. I detected the X table lift using the indicator. The needle would pop up during direction changes and return to normal.

For the Z square I used an old fashioned builders square and a collet wrench with the dial indicator. I'll see if I can find the thread but it is used much in the way you describe the round calibration plate.

You also have to remember, these are not milling machines. You will drive yourself nuts trying to get all the error out you can see with a dial indicator and then you'll go insane trying to keep it. My goal was to reach acceptable. The needle still jumps around and the Z is actually still out of square depending on where it is measured along the gantry. There is actually still roughly a .003 lift in the table during direction changes. If anybody gets a buddy to be more than 1/256th accurate and can KEEP it my hat goes off to them. I doubt after it is moved and runs a while it will remain that accurate. But even if it dropped to 1/128th it is very acceptable.

That said, your points are valid. A set of tools and/or adhoc contrivances for calibrating and seeking error are very valuable to have around.

/RB

dubliner
11-10-2009, 03:37 PM
Awesome work Robert, I havent had any problems but I know who I'll be calling if I do :-), Hope youre well - Nev

harryball
11-17-2009, 05:54 PM
Marty has his machine in his shop! This should make a good closure to this thread.

With the 20T pinions the top end cut speed seems good at about 2 ips and a jog of 3.5 or so. These are not hard numbers but seem the most comfortable for his machine. I did not really try to push it further and I doubt it would go much faster before giving problems. I don't know the original speed it was capable of but Marty cuts around 1.5 ips and slower.

It sounds different while moving but that was not unexpected.

Overall I think it will accomplish what Marty needs without an issue.

/RB

harryball
11-17-2009, 06:07 PM
Someone asked how to set the accuracy from 6dp to 4dp. With VCarve Pro (PartWorks) or Aspire you need to edit your Post Processor of choice.

Find lines that look like this...
var X_POSITION = [X|A||1.6]
var Y_POSITION = [Y|A||1.6]
var Z_POSITION = [Z|A||1.6]

And make them look like this...
var X_POSITION = [X|A||1.4]
var Y_POSITION = [Y|A||1.4]
var Z_POSITION = [Z|A||1.4]

If you do search and replace be careful to specify enough so you don't catch other values or verify each replacement before it occurs.

I have no idea why this improved the outcome, it wasn't much but it did help. Since it didn't hurt I left it.

/RB

rb99
11-17-2009, 07:21 PM
Good job!

beacon14
11-18-2009, 01:27 AM
Now that's perseverance - all done the same year.

Nice work Harry.

B. Pile
04-10-2014, 03:09 PM
I am posting in this thread because I believe my problem is relative. However, the machine I am running is a PRS Alpha. After reviewing this thread a tried my best to relate the two. I readjusted the concentric bearings on the X and checked for play in the z and y also. Each coordinate felt solid - no play. The problem: when vcarving the internal corners are finished sloppy. I've attached a picture to show my results. This problem has occurred out of the blue recently. I would also like to add my machine gets moved to new locations often but has never been a problem before.

I appreciate any help

Thanks, Cody

Gary Campbell
04-10-2014, 10:13 PM
Cody...
That looks so uniform that I might guess that you are using a V bit that is a different angle than is stored in the database. Call tomorrow if you cant figure it out.