mistermikev

1 minute ago, curtisa said:

Not suggesting there's anything wrong with adding limit switches to improve accuracy - it certainly does just that. But there may be some confusion as to what a repeatable home position actually does compared to backlash.

Backlash is primarily what happens when an axis reverses direction and there's a dead spot in the rotation of the stepper motor before the axis starts moving in response to the stepper's rotation.

Imagine the tool is at X=0. The software tells the machine to go to X=1. The axis motor turns, but because theres a bit of slop somewhere (loose coupling, stretchy belts, slogged-out leadscrews etc) the first couple of rotational steps of the motor does nothing to the axis until the slop takes up, and only then the axis starts moving. It eventually only makes it to X=0.98 but the software thinks it's at X=1. Depending on how bad the backlash is, including if it's asymmetric, the error can compound the further the tool moves from the starting position.

Adding home/limit switches makes home consistent, but doesn't help once the tool needs to move away from home.

so... not challenging at all... I just want to make sure I understand.  right so... machine moves to x=1 but has really only moved .98... then machine moves to x=0 but there is a different amount of backlash/slop-in-the-ball-screw... and it moves .9... now x=0 is .1 away from where it should be.  In theory this is all compensated for via an avg when setting your cycles/steps... and in practice on my machine it's not a measurable difference... as repeating a move against a dro... (admittedly w/o work piece resistance) I get the sm result multiple times... but in theory this could happen, no?

42 minutes ago, curtisa said:

Limit switches will only provide a relative reference for your machine for all subsequent operations. There are a lot of other ways for a front/back operation to fall out of alignment that limit switches alone will not correct:

• Backlash on axes (if any) cannot be compensated using limit switches and may result in the tool being further away from the commanded position than the CNC software thinks it is, which will translate to misalignment from front to back when the workpiece is flipped over.
• If the north-south travel (Y) is not perfectly perpendicular to the east-west (X) travel you'll see misalignment. Same problem will exist if the Z-axis is not perfectly perpendicular to the CNC bed.
• Rigidity of the CNC frame and components (and any flex in the tool, particularly if it's long and sticks out a long way from the spindle) will upset front/back alignment
• You don't mention which kind of Shapeoko you're using, but I wouldn't trust any of the versions that use belts to be extremely reliable for this kind of work. Belts may stretch over time which will ruin repeatability and hence front/back alignment. Ball screws will yield more accurate, repeatable results for this kind of work.
• etc...

Many ways to skin the cat, but here's how I do it (assuming I've dialed in as much perpendicularity, rigidity and squareness into the machine before starting):

1. I use a dedicated fixture board that is rigidly bolted to the bed such that it cannot move. A simple G-code is used to machine four locating holes into the board at each corner outside the perimeter of the body that will be machined, plus a centre line is machined into the fixture board (MDF is OK). This only needs to be done once.
2. Using a sharp vee bit (60deg tip angle) I align the CNC tool tip with the bottom of the centre line on the fixture board and touch off X and Y axes as accurately as I can. Do not power-off or reset the machine.
3. Take body blank (assuming it's already as flat as possible with front/back faces as co-planar as possible) and mark a centre line. Extend the ends of the centre line down the edges too.
4. Remove the vee bit from the machine and clamp body blank on table, lining up the centre line marked on the blank with the centre line on the fixture board.
5. Install bit into spindle and touch off Z axis on the body blank.
6. Using the same code that generated the four locating pins in the fixture board (step 1) machine four matching locating holes into the body blank.
7. Remove the body blank from the CNC and install four pins (eg dowells, steel pins etc) into the four locating holes and align them with the four holes in the fixture board. They need to be a snug fit.
8. Run the same code that made the four pin holes in step 6 on the other side of the body blank.
9. Machine the body blank using your required tools and operations (can be either front or back - take your pick).
10. Once done flip the blank over, install the four pins on the other side and clamp to fixture board.
11. Machine the opposite side of the body blank using your appropriate tools and operations.

Using the above method I've been able to achieve alignment to within half a mm or less from front to back.

so... first off - I appreciate that there is some good info here.  I hadn't thought of mentioning tramming, nor tightness of index pins, nor machine flex.

For context of my post op - I've learned a lot from curtisa and mikro.  their advice > my advice.  Really a novice here as I started cnc just a couple years ago.

many points that I instinctively use from above comments... for ex my spoil board is quality baltic birch and some 20+ (nylon) bolts.  when I built my spoilboard: I home my machine, setup/saved my offset, use a v bit to align initially.... drilled all bolt holes, then mounted, then drilled my index holes, then planed the surface.  that should all be relative to my offset.

but when doing index holes in my piece - I use a 3" bit to cut all the way through.  now... I've trammed my machine to .007 tolerance.  is there something i'm missing that you would drill index pins from either side as opposed to just straight thru.?  On the one hand that would avoid any error in the bit/collet... but if it's trammed that has to be a very small amount.

also... I mention backlash in my post.  and I say that homing is a correction for it, which your statement contradicts.  if I am wrong I'd like to understand why... but I was trying to point out that if you run a big 3 hour operation and potentially introduce some backlash error... you can then re-home and go to your offset - you'll be back to actual zero within the tolerances of your limit switches... effectively negating the backlash error. 

11 minutes ago, Bizman62 said:

For paint that most likely would require some primer that's made for wood, and that should then be suitable for car paint.

That said, the ultra clear 2k which is intended for metal flake paint seems to work perfectly well on guitars.

right, that was kind of my point... you need a primer that is made for wood that is also compatible with a paint that is typically intended for metal... idk what the market is like today but 20+ years ago when I did this with my brother... it essentially meant finding a car paint guy who knows something about wood or a guitar paint guy who knows something about cars... and internet wasn't nearly as much of a resource back then so... might have been a much bigger long shot... but I thought I'd mention it because a car paint person might not really be aware of the issues of priming wood. 

Can certainly ask your car person if they will work with other paints... and frankly back in the day(20s thru the 50s) all cars were painted with nitro lacquer... but I just pointed that out to say that the typical paints used today for cars may or may not necc be compatible with the typical primers that are made for wood.

my brother is an auto body expert... works as a mechanic but his passion is restoring old cars.  he's done a number of show cars.  a long long time ago he repainted two guitars for me... and they were about as good as a finish can be... very pretty.  the finish didn't have great adherence/duribliity to the wood... so I guess that would be one thing I would watch out for there.  

as much as my elbow hates wet sanding... my approach to your problem has just been to try and make it easier for me to finish and I have learned that a job can be a LOT easier if it's prepped well.  I haven't bought a da sander yet (requires a large compressor) but I can tell you that that is how 90% of auto body finishes are done.  when you've got to get a flat surface on a huge area like a car... that is THE tool for the job. they (I'm told) also do a great job of buffing. 

In the interest of getting closer to the functionality of a da sander I bought a bosch cordless sander that, similar to the festool or other elec da sander... puts your hand very close to the sanding surface... and haven't used it on a finish yet... but i can confirm it feels just like a da sander for doing basic sanding.  I'm hopeful it will make things easier when it comes to wet sanding.  Not many sanders I would trust to wet sand on a contoured surface... but a da sander can def do that.  will have to snag some mesh sanding pads in the 1200 and up grit... and will report back when I get there.

hope there is something there you can use!

On 9/5/2023 at 8:46 AM, jeremiah.peschka said:

Long time lurker, first time caller...

I've been learning CNC to build guitars, but one thing that's been a frustration is getting two-sided builds to come out with virtually no misalignment.

Historically, I've had a few missteps that have resulted in significant misalignment. Today's process is:

• Placing the blank on the CNC.
• Drilling two holes along the center line (ish)
• Placing the blank on a pair of fixturing pins in a fixture plate from Saunders Machine Works.
• Securing the blank so it doesn't wander.
• Setting zero based on the top and center of the material. I'm finding the center by going corner to corner.

Unfortunately, there's still 1/8" - 1/16" misalignment between the top and bottom of the body. It's not awful and can be taken off with a table router, but I'm wondering:

How do y'all ensure that you can reliably flip a guitar on the CNC so you can do two-sided work?

well... I wouldn't say that I'm an expert on this subject... as I've had varying degrees of success... but I have learned a lot lately. 

Just using my eyes and a center line and going to the back, align, then going to the front and align... I was able to get within 3/16. 

I've since started using 4 index pins... but I was drilling index holes and then flattening my stock after... and this got me to 1/8" accuracy.  This was all w/o using limit switches. 

Now I've setup my limit switches and a light has gone on... used to always worry about finding my ctr after pwr outtage before... no longer an issue.  I have yet to cut another two sided body/neck since I've set this all up but I'm pretty confident things will have improved.  my index holes are now standardized and drilled into my spoilboard -cut after homing my machine and then setting up on offset on the offsets page.  I've have verified that my bit will go back to exact ctr every time now.  so even if I bang it off the walls... I can home the machine, then select my offset... and it will go back to the EXACT center I set.  

So many folks tried to tell me to do this... I wish I had listened sooner.

so much can go wrong that you don't think about when building.  if you run into the walls... you've changed your center... a machine can loose a step here or there and it will look some precision on the center,  backlash in your machine can change your center.  altho in theory none of this should happen...  all of this is corrected by using limit switches, and setting up an offset because the machine will find your center again reliably.  

hope something there helps.

right on, the older I get... the more relevant the statement "I'm still alive" is!  Have taken a bit of diversion lately... but it's just about time to get back to it.  

that paudauk? looking pretty sweet.  some tidy work there.

2 minutes ago, ShatnersBassoon said:

At some point I would like to make a lightweight electric carbon fiber guitar, using the fabric in a mold. Not the glued panel technique I currently use. For example a build like the Rubato Lassie. Although my current way of working with CF produces some cool results, I would like to do something more economical and streamlined.

that is certainly a worthy goal.  I have oft thought why you just don't see a lot of fiberglass construction.  I believe the mosrite stuff (or some similar guitar) was all fiberglass... and there was a guy here on this forum that was doing some fiberglass... but it's just not common.

carbon fiber would def be cool too.  I loved the idea that parker was doing with the thin fiberglass over hardwood.  made for some impossibly thin/light guitars that were very stable and sounded great.  

anywho, here's to seeing you realize that.

wow, looking sharp.

thank you for the compliment.  can't go wrong w purpleheart imo.  should make for a pretty lil gtr.  purpleheart bridge might pair nicely - just sayin'!

On 8/20/2023 at 12:32 PM, killemall8 said:

Ive had this problem on 90% of necks ive ever made.
Regardless of the method of radiusing, including pre radiused boards.
 

With fretboard glued to the neck, either radiused or flat. 8" sanding block or 20".

Fretboard dead flat, with 4 different straight edges.
use either long or short sanding block. 5 passes with it, already a hump in the middle.
Blocks are flat and straight measured with precision straight edge.

I dont understand how people can just clamp a neck to a table, radius with a short block and it be fine.
Ive tried so many d ifferent methods to avoid this and none do anything.

I have to go back and manually knock down the middle and it takes forever.
How do you avoid this and do you have any ideas of why this happens?

With a long sanding beam it doenst seem like it should even be possible.

afraid I can't add much here... but I'll commiserate.  sanding is really hard.  I try to avoid it at all costs.  to sand fast and true... you need to use less pressure.  I know that's the case but I have somehow yet to learn it.  we all put pressure on... and when you do that it's not going to be even.  

I know folks sand fretboards with blocks... and I would assume some can do it well... but for me it is a lost cause.  The only guaranteed solution is to make it mechanized.  one strategy would be to build the common radius router jig. 

Another technique I've seen... warmoth I believe is where I saw it... they have a 2' long flat sander and they have a jig that is mounted to the ceiling on rope... they mount the fretboard and it just makes contact with the sander... move it to and fro and voilla... radius fretboard.  Theirs was actually setup to do compound radius via dif lengths at either end of the fretboard. probably hard to dial a system like that in.  

hoping you find some sort of useful pea in this comment.

was going to tell you "that's crazy talk... it'll never work" but I guess i'm a little late (jk, wasn't going to tell you that).  I don't believe I have seen a headless classical until now... pretty cool.  nice work.

5 minutes ago, henrim said:

Thanks. To me it shows that I can’t really do it anymore as I used to. In the beginning of the 90’s I started to study industrial design and my aim was to become an automotive designer. I drew cars and motorcycles all the time. As a first year student I read a book written by Victor Papanek in the 70’s: Design for the Real World: Human Ecology and Social Change. That was total game changer and I realized there was much more to it, and didn’t want to become a car designer any more. Anyway, I still doodled vehicles for many years. I still do that sometimes but not very often. 

when I was a kid... maybe 10 or 11 years old... was really into art/drawing/painting.  I used to draw cars all the time.  mostly just sideview.  later in life progressed to 3d lol.  I have some old paintings of guitars and cars that I've kept over the years... it's fun to look back on that from time to time.  Your picture reminded me of those days... youth and nostalgia.  

"and social change"  wonder if I missed any books on "data structures and social change".  "discrete mathematics and social change" lol.

i just came in here to accomplish two things...

#1 wanted to suggest to @Andyjr1515 that it might be time to take your medication based on your first sentence lol.  (jk, love seeing that gtr again btw)

#2 welfare check on(harrassment) @stu chop chop brutha!  them geetars ain't gonna make themselves!  looking over the thread... it's a really nice carve and a sharp guitar.

somewhere I saw this guy from brazil that makes these really cool one piece guitars and they are  all scuplted and hollow... very unorthadox approach but he apparently takes a thin bandsaw blade, cuts the body in half, hollows it out... and glues them back together.  He somehow does this with little to no seam.  not sure I'd have the skill to pull that off but I'd like to see someone else do it so... just thought I'd mention lol.

wow dude, that car is a really great drawing.  nice work.  

that's an interesting piece of wood.  It would look really cool with a "weathered motif".  or even take a page out of the prs catalog and tape it off based on the spalt lines and do a "partial dye".  

anywho, neat stuff.

18 hours ago, ScottR said:

I may have mentioned this in the past, but I truly enjoy making necks!

SR

it shows.  man... that purple hue... just lovely.  nice work.

nice looking design.  rawk on.

reading this I can't help but think about what a build would have looked like if I had done one when i was 14... i suspect it would have been horrific.  cudos to you... your's has some pizazz.

ballsy approach to covering the hole... if it were me I'd just put a cool veneer on the back side... but seems like you've come out ok either way.

poly really is a difficult finish to do gloss w imo.  if you cut through any layer and then look at it in the light... you'll have witness lines.  So each coat has to be so thick that you won't wetsand thru... and more importantly the target has to be absolutely flat... or the coat will have to be even thicker, that you don't wetsand thru despite an irregular surface.  and if you put on a thick coat you'll have that much more wet sanding to do.  vicious cycle.

just my 2 cents but once you have witness lines... not much you can do.  if I was gonna do a gloss by hand... I'd use nitro.  Each layer melts into the next layer so you just need to build it up thick enough and then wetsand to flat after it has cured for 4 weeks.

all that said, never met a tele I didn't like.  is a handsome body.  nice work.

6 hours ago, ScottR said:

All those tiny pieces......makes my eyeballs twitch.

SR

on the one hand... it's a bit like diffusing a bomb... on the other it's pretty grattifying!

2 hours ago, ScottR said:

Holy crap, that's ambitious!

SR

You see many of those in Arizona?

sr

hehe... well I'm finding with inlay... that going small is more ambitious than going large.  I should have shown my finger next to this but... it is small enough to fit on a headstock anyway.  I feel like "this is what an archeologist must feel like" carefully cutting/scraping and blowing gentle on the pieces as I remove them from the block they were cut from.  Tedious.  If you cut too deep... the wind from the router will toss the piece into oblivion... and if you cut too shallow... you'll never get it out.  Fun times!

Because it's so small... some of the details (fins) I planned to implement via scoring and filling with some ebony dust or black ca glue.  S/B a good learning experience anyway.

anywho, here in az... all over the place there are signs for "so-and-so river" and "so-and-so lake" and you roll up on it and it's just like the rest of the desert you see - dry as hell!  Feels like a ripoff... then it rains and surprise they weren't lying!  Have never been fishing here... and I'm told there are great places to do it... but I imagine half of your fishing trips end up at a puddle that used to be a lake!  So the great arizona marlin will have to remain unconfirmed hehe.

minor update... ac went out today and I think I have heatstroke... was 90 in here all day long.  so I had hoped to get some work done today... but only managed this so far:

2 minutes ago, ScottR said:

Yeah, rosewood is wonderful stuff.

Did you ever pick up any of your local Arizona Rosewood?

SR

matter of fact I did.  have a chunk sitting there and was thinking I might use it for yet another les paul.  

rosewood... ah yes... that purple... beautiful stuff!

wow, so many colors in the back of that headstock.  v cool.