Deflection in Outline Cutting-Looking for Input Please!

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JohnLashuay
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Deflection in Outline Cutting-Looking for Input Please!

Post by JohnLashuay »

Hi All!

We are using a 3/8" Compression bit to outline cut plywoods and melamines. What we have found is that when it double passes the deflection tends to be greater therefore causing the need to hand route these pieces to clean them up. Our remedy for this is to "climb" cut jobs that have a lot of double pass parts. The problem is that the single pass parts tend to not be as cleanly cut (a little fuzzy).

What is the possibility of being able to add an option to "climb cut" double pass parts and keep single pass parts "conventionally cut?"

Any feedback would be appreciated!

-John
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by Josh Rayburn »

John,
The only other thing you can do is to max pen the tool at half the material thickness, this will cause significantly less deflection.
You probably don't want to slow the tool down, because that's just going to cook it.
The problem is that this would of course cause ALL parts to be "double passed" according to the max pen, regardless of the parts' sizes.
Probably not helpful, but if you need to isolate parts that are problematic, you could try that strategy.
jnr
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by JohnLashuay »

Thanks Josh!
I'd rather not cut in only half way. I am concerned that it would not hold down well enough.

Do you do much cutting of small parts that need to be double passed? If so are you getting the these results?

-John
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by Josh Rayburn »

Hi John,
Yes, I've cut lots of everything big and small!
Hold down is always a concern on the real tiny stuff, but the double pass feature has worked very well. I have a 25hp vacuum pump and it does the job very well.
I generally cut MDF core materials in two passes in a climb direction no matter what to make up for the deflection, but on veneer core materials, which have to be cut conventional to avoid the fuzz, it can be noticeable.
What feed speeds are you running at and what is your vacuum size? Also what thickness are you leaving the skin for your double pass parts?
If you run the tools into the ground, you've probably noticed how essential it is to re-tool for VC materials as well....

Another note, the tabbing feature in CN could use a little work - but a little birdie told me that this might get some attention in the future, just don't know exactly when. I've cut lots of V-Carve stuff too - and the Vectric tabbing feature is AWESOME and works very well, so hopefully if it's anything like that, then that might be a more practical and faster-machining-time solution in the future.
jnr
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by JohnLashuay »

Josh Rayburn wrote:What feed speeds are you running at and what is your vacuum size?
our speeds are down around 400-500 depending on the tool
our vacuum pump is 18hp
Josh Rayburn wrote:Also what thickness are you leaving the skin for your double pass parts?
we leave .020"
Josh Rayburn wrote:If you run the tools into the ground, you've probably noticed how essential it is to re-tool for VC materials as well....
We have been careful about this because we have seen additional deflection the more the tool dulls.
Josh Rayburn wrote:Another note, the tabbing feature in CN could use a little work - but a little birdie told me that this might get some attention in the future, just don't know exactly when. I've cut lots of V-Carve stuff too - and the Vectric tabbing feature is AWESOME and works very well, so hopefully if it's anything like that, then that might be a more practical and faster-machining-time solution in the future.
jnr
We haven't looked into this feature yet.

Do you cut much with melamine?

-John
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by Josh Rayburn »

Tons of melamine. Literally :)
The melamine holds down much better since it's got a clean face that the air does not suck through, as I'm sure you've noticed too.
It is tough when the part is so small that it doesn't cut the skin at all, it gets a little messy. But, I make parts for other shops, so they all have a tablesaw and they are happy to deal with the real small stuff - the saw is the right tool for those jobs anyway.
jnr
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by JohnLashuay »

We cut a lot of drawer boxes and we need to double pass about 90% of the parts. Because we blind dado our drawers, the saw is no longer an option (big reason for getting the cnc).

This is the main reason for the question. In order get the best yield, we try to nest the drawer parts into a job. This is where it would be great to be able to have an option for climb cutting the double pass parts only and conventional cutting on the single pass parts.

Would this option be a benefit to you?

-John
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by Josh Rayburn »

John,
Yes, that would be beneficial.
I'd really love to see the first pass (climb or conventional) leaving a skin, but OFF THE LINE by a user defined distance. Then the final pass could graze the edges and go through all the way. This way it does not matter what direction or material we're cutting, we know the deflection is gone because we're only grazing .020 off the outline on the final pass, and we get the cut direction we want. I've used this for DXF parts successfully for a long time.

As far as the drawer box parts, I rarely have anything move around on typical size boxes, i.e. 4" drawers are about the smallest I have to deal with on a regular basis.
jnr
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by JohnLashuay »

That sounds great! That would allow a very small load on the tool which should reduce the deflection, right?
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by Josh Rayburn »

Exactly. That's the ticket to parts with square edges and clean cuts.
Solids are much different, you can't take that approach or you'll get stuff tearing out all over the place, but it works perfectly for sheet goods. I only cut solids from DXF - manually programmed anyway.
jnr
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by Gary Campbell »

Hey guys...
This conversation is a surprise to me as a ShopBot user. I cut a good number of parts using the SB Link. Due to greatly reduced vacuum capabilities and much greater machine deflection, most ShopBotters need all the help we can get to keep parts from moving and the correct size.

In the link, which I assume is a subset of your CN software, we are able to select "run opposite direction" for our final (skin removal) outline pass. Most of us run climb for the first pass, (or passes depending on settings) and then do a conventional (no load) pass to remove the skin. This seems to be the best of both worlds for our cutting needs. Deflection on cutting passes is into the waste, and final conventional passes are at little or no lead for very accurate parts with great edge quality.

I do dadoed (and blind) solid wood drawer parts using this method, tho some porous species like Oak, require leaving the skin on to be removed with a lam trimmer.

I am sure there is a terminology gap between our respective user groups, so please pardon my question of the obvious. John,when you say double pass, are you referring to a pass to skin depth and then the skin removal pass, or 2 less than full depth passes? My usual cutting for 3/4 ply or melamine is climb @ 400 ipm to .035 skin and same speed conventional to remove skin. Thanks for your time and sorry to interupt.
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by JohnLashuay »

Hi Gary! No need for apologies...thank you for your input!
Gary Campbell wrote:In the link, which I assume is a subset of your CN software, we are able to select "run opposite direction" for our final (skin removal) outline pass. Most of us run climb for the first pass, (or passes depending on settings) and then do a conventional (no load) pass to remove the skin. This seems to be the best of both worlds for our cutting needs. Deflection on cutting passes is into the waste, and final conventional passes are at little or no lead for very accurate parts with great edge quality.
This sounds like what I am looking for.
Gary Campbell wrote:John,when you say double pass, are you referring to a pass to skin depth and then the skin removal pass, or 2 less than full depth passes?
Yes, a double pass goes to a set skin depth. For us it is .02"

Thanks again Gary!
-John
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by Jeremy Schiffer »

Definitely count my vote on this one. That lip on double-pass parts is annoying, and either of those solutions (user-configurable "oversize cut" on the first pass, or a climb on first pass and conventional on second pass) would be greatly appreciated! It's no fun having to go back after the CNC to clean up edges by hand!
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by Keith Neal »

Count my vote as well, we cut mostly solid surface on our machine, it's hard to get a tight seam on the smaller pieces when they are double passed, the same for our 3cm material which needs to be cut in multiple passes due to thickness and density(otherwise we'd have to use a new bit for every sheet)-Keith
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Re: Deflection in Outline Cutting-Looking for Input Please!

Post by Gary Campbell »

Guys...
The "run opposite direction" for skin removal pass is an awesome feature. I lobbied long and hard for that one. I just assumed that your "big iron" didnt need the feature. I hope the programmer crew wont be miffed I let the cat out of the bag. But I bet they have a couple extra checkboxes laying around in a desk drawer for you guys.

Currently we are hoping to get a selectable cut order to allow drilling and dado cuts before PE thru cuts. This will afford those of us with small vac pumps to cut all the depth critical geometry before thru cuts start reducing the hold down, especially on plywood. Doesnt seem to affect melamine as much due to it is a flatter product. On some parts that have more PE cuts than others the tenon thickness is all over the place.
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