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so... cnc body joining?


mistermikev
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so was thinking about setting up to do a body join on my cnc. 

I typically do it now using a 3" long 3/4" diameter cutter in my hand held router with a top bearing... yeah... it's a bit crazy.  I generally am just barely taking off 1/32 at a pass but even that is pretty dangerous.  I am careful not to choke the router and it does fine... but I'd rather just do it with my cnc if possible.  It'd be safer and even if I just do an initial cut with the cnc it will even out the material right at the grain line I want it at... and worste case I can do a final pass with the hand held.

My cnc doesn't accept anything bigger than 1/4 bits.  (no, not talking about 1 pass with the cnc.. this would still be .08" passes).  In order to do this...  I'd have to buy a longer bit.  I also would need some bigger hold downs.  So before I go spending money on this adventure... I thought I'd get any input you'd be willing to give.  ever try it?

if I'm going ahead... I know that bigger diameter bits - the cutting edge is going faster... and with the momentum of the extra metal - they tend to cut better/smoother.  That said... a sharper bit would leave a much nicer edge.  My spindle can handle the bigger bits, but I'm not sure that's necc the way to go.  I don't want to spend more than $40 on a bit and it'd have to be at least 2.75" tip to toe. 

what say you?  fools errand?

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18 hours ago, mistermikev said:

ever try it?

Hadn't actually considered it. TBH I still joint the traditional way - jointer, handplanes, sandpaper on a flat surface. The amount of time it'd take me to set up and run the CNC for a facing operation on two surfaces would probably take me just as long.

I suppose if you're only looking to take off max 1/32" in 0.08" passes, you'd have to weigh up whether it was worth your effort and time to do it semi-autonomously on the CNC. Say you're jointing two pieces of timber 1.75" thick over 18" and running, I dunno, 50 IPM?:

  • 18" / 50IPM x 60s =21.6sec per pass
  • 1.75" / 0.08" = 22-ish layers to remove to reach the bottom of the cut (assuming you're cutting in both directions)
  • 21.6sec x 22 / 60sec = 8min to joint one edge.
  • Setup time (clamping down, aligning, zeroing, touching off, unclamping etc) maybe 10min per piece?
  • Coding time maybe 15min?

(8 x 2) + (10 x 2) + 15 = 51min.

That's assuming your raw stock is straight and square enough such that it only takes one pass to fully joint each face. If you've already managed to get the raw stock that close off the saw or from the timber supplier, I reckon you could probably joint by hand in about three-quarters of that time.

 

18 hours ago, mistermikev said:

it'd have to be at least 2.75" tip to toe

That's pretty long for a 1/4" shank bit. The longest one I have is 2.25" and the amount of 'singing' it does when making long-reaching cuts makes me nervous sometimes. Bit flex and any errors in spindle runout and eccentricity get amplified when the bit sticks out a long way beyond the collet. I personally wouldn't want to go any longer without switching to a bit with a bigger shank.

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9 minutes ago, curtisa said:

Hadn't actually considered it. TBH I still joint the traditional way - jointer, handplanes, sandpaper on a flat surface. The amount of time it'd take me to set up and run the CNC for a facing operation on two surfaces would probably take me just as long.

I suppose if you're only looking to take off max 1/32" in 0.08" passes, you'd have to weigh up whether it was worth your effort and time to do it semi-autonomously on the CNC. Say you're jointing two pieces of timber 1.75" thick over 18" and running, I dunno, 50 IPM?:

  • 18" / 50IPM x 60s =21.6sec per pass
  • 1.75" / 0.08" = 22-ish layers to remove to reach the bottom of the cut (assuming you're cutting in both directions)
  • 21.6sec x 22 / 60sec = 8min to joint one edge.
  • Setup time (clamping down, aligning, zeroing, touching off, unclamping etc) maybe 10min per piece?
  • Coding time maybe 15min?

(8 x 2) + (10 x 2) + 15 = 51min.

That's assuming your raw stock is straight and square enough such that it only takes one pass to fully joint each face. If you've already managed to get the raw stock that close off the saw or from the timber supplier, I reckon you could probably joint by hand in about three-quarters of that time.

 

That's pretty long for a 1/4" shank bit. The longest one I have is 2.25" and the amount of 'singing' it does when making long-reaching cuts makes me nervous sometimes. Bit flex and any errors in spindle runout and eccentricity get amplified when the bit sticks out a long way beyond the collet. I personally wouldn't want to go any longer without switching to a bit with a bigger shank.

all good points there.  I think I typically do 80ipm but still that take a fairly long time.  That said... I have a camera and can spend that time at my pc jacking around with other things.  Further, if I was going to do it regularly I could setup a jig I could just mount and fire off.

is it worth it - yeah, probably not. 

the bit length... currently my bit sticks out 1 5/8" and I've used all of that without issue nor noise.  Literally had her up to the hilt and hand on the stop button in case there was still one pass left!!    I would just need to get to 2" of cutter below the collet but I like to have my bit at least sticking out of the back side of that collet a little bit. 

further.. I don't know if this is crazy talk... but was thinking that if I do one pass in .08 increments... and had a bit with 2" of flute... and then moved my x by 1/64"... I bet I could get a pretty solid join.  Any mistake would be certain disaster tho so... I dunno.  

thank you very much for your wisdom sir.

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6 hours ago, mistermikev said:

is it worth it - yeah, probably not. 

I wouldn't go so far as to say it's not worth it. Any new technique that changes the way you do something to make a process safer is worth it, even if it takes longer. I guess I'm more looking at it coming from the angle of doing the jointing differently to begin with, and reserving the fancier tool for the fancier job. Pick your fights, if you know what I mean ;)

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6 hours ago, curtisa said:

I wouldn't go so far as to say it's not worth it. Any new technique that changes the way you do something to make a process safer is worth it, even if it takes longer. I guess I'm more looking at it coming from the angle of doing the jointing differently to begin with, and reserving the fancier tool for the fancier job. Pick your fights, if you know what I mean ;)

well one of the things I thought it would buy me... is that usually when I cut with my router it takes a few tries to get a good join.  however I typically draw a line of where I want the grain to be cut for a good match.  so I rarely get exactly what I wanted after I cut a few times.  with the cnc, in theory it should be good first time thru... so it might actually give me a better result.  or at least a more predictable result.  

if/when/someday I will upgrade my spindle to one that accepts a half inch bit... that would def make it a sure thing.  bigger longer bit.  anyway... something to think about!

thanks again for your input!

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look at shars.com. cutting tools square end mills go to bottom of the left side for lengths

https://www.shars.com/products/cutting/end-mills?cutting_diameter=1%2F4&end_mill_category=Square+End&overall_length=4

even though the flute lengths are only 1". so It is imperative that you are trammed correctly. I use the 3 " in 1/8" Ball nose for drilling through holes  on hardtail bodies

mk

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19 minutes ago, MiKro said:

look at shars.com. cutting tools square end mills go to bottom of the left side for lengths

https://www.shars.com/products/cutting/end-mills?cutting_diameter=1%2F4&end_mill_category=Square+End&overall_length=4

even though the flute lengths are only 1". so It is imperative that you are trammed correctly. I use the 3 " in 1/8" Ball nose for drilling through holes  on hardtail bodies

mk

fantastic resource.  I'm going to have to place an order with them.  thank you so much for sharing!  hey also - happy new year!  good things your way in the new year - I hope you wife is doing good and hope you are surviving taking care of her!!

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1 hour ago, MiKro said:

Another thing is this when cutting the edge of the center line with your CNC do each edge on the opposite side of your cutter. This will take in account any possible tramming issues in that axis. Similar to cutting a piece in two if that makes since?

MK

cut.pdf 42.47 kB · 2 downloads

cut.jpg

1 hour ago, MiKro said:

Another thing is this when cutting the edge of the center line with your CNC do each edge on the opposite side of your cutter. This will take in account any possible tramming issues in that axis. Similar to cutting a piece in two if that makes since?

MK

cut.pdfUnavailable

cut.jpg

makes perfect sense.  It'd be nice to cut both sides at once and mirror any chatter but that could get dangerous pretty quick.   Think I'm going to try some version of this on my next blank glue up. 

was thinking... it'd be really cool if I could get it going with the cnc and get comfy with it.  then instead of doing a straight cut... follow the grain pattern.  do a mirrored cut on the other side... hopefully following a grain line as well.  then joining them should disappear pretty easily.  Something to think about anyway!

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