Poor quality finishing

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Poor quality finishing

Postby Greg » Thu Apr 27, 2017 5:48 am

I made the change from using cut3d to mesh cam and I am experiencing some poor quality finishes. I am running a 4 flute spiral cutter. the roughing pass is 1/8" DOC at 80 IPM. My finishing pass depth is .020 with an overlap of 12% at 80IPM. Please view the photos and if anyone has any recommendations they would be greatly appreciated.
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Please notice deep cuts that did not get taken out with the finishing pass
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IMG_2476.JPG (110.58 KiB) Viewed 537 times
Greg
 
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Re: Poor quality finishing

Postby Arlen » Thu Apr 27, 2017 2:00 pm

Greeg wrote:I made the change from using cut3d to mesh cam and I am experiencing some poor quality finishes. I am running a 4 flute spiral cutter. the roughing pass is 1/8" DOC at 80 IPM. My finishing pass depth is .020 with an overlap of 12% at 80IPM. Please view the review and if anyone has any recommendations they would be greatly appreciated.


It doesn't look too bad, you could try going over it with some sand paper.
Last edited by Arlen on Sat Sep 16, 2017 4:37 pm, edited 2 times in total.
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Re: Poor quality finishing

Postby larynx » Tue May 02, 2017 2:54 pm

Greg,

You do not state if you use one finishing "pass" or multiple nor what settings are used in [if used] waterline finishing. An overlap of 12%, as stated, should tell me that you are using [bit?], lets say a 1/4" bit [again - end or ball mill ?] with stepover of 0.030" - which over contours may/may not be fine depending upon your finish pass[s] settings.

Upon viewing your images, all I can state is that it appears I see cutter lines spaced out as if a waterline is being cut with a ball mill at much greater than 12% stepover. I have had such appearance in some of my cuts that I used looser than normal settings in order to speed up a cut to produce a "sort-of-will-look-like-this" prototype. I have also cut pieces that required absolutely no sanding at all, with a factory finish look.

Are perhaps you using an end mill and not a ball mill for finishing these 3d curves?

I may not be the best one to respond, I see not many responses, I read everything on the forum I can - great resource and a wake up - so thought I'd give it a shot. I do - personal experience - know MeshCAM is more than capable of producing much better results. I have actually cut items with complex shapes that were "finished" after the cut was completed. No sanding, just liquid finishing. Yes, they take a lot longer to cut, but the final product was spectacular. EG: finishing with 1/2" ball mill, 0.012 stepover, X&Y parallel, waterline. Trust me, those cuts take a while, but the results are such that no sanding is required, no change in CAD designed shape, within a sub thousandth of design. Many would tell me that is too much, too fine, the result will not be any different than a wider 0.030 stepover.

And yes, that is much too fine for most cutting. But when finish is paramount and I do not wish to invoke my sanding skills and possibly change the shape from drawing even 0.001, that's what I do. It works so I use it, no second guessing, better too much in that case than too little. But I will reiterate - I use those settings rarely and on few parts. But oh my.......that piece of wood looks like a sculpture.

You need to play a little to find your sweet spot for what you want. I would suggest changing your settings a little at a time - perhaps 10% until you are happy. Place a piece of wood and start cutting. When completed, before you remove the piece from your table, if not happy, recalculate in MeshCAM with "tighter" settings and recut while in place, not yet moved. Everything should be fine and you only need to calculate another finish cut. Like sanding, with the machine. Rinse, repeat, until happy. Keep a log. One thing you also did not mention, time to cut. If the bit used and times are close to the same - Cut3D versus MeshCAM, the end product should be close if using the same settings. At least it makes sense to me.

Good luck.
I am not aligned with nor do I have any relationship with MeshCAM or its staff other than being a user [that sounds a little like I have a dependency problem]
larynx
 
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Re: Poor quality finishing

Postby Doug » Thu May 04, 2017 10:43 am

Hi Greg.

You haven't provided enough information to judge (e.g. cutter diameter and type) therefore all I can do is show you what I achieved recently and quote my parameters so you can compare. I recommend a ball nose two flute 1/4" mill for finishing. Your picture looks like only a roughing pass has been done!

What you have quoted looks reasonable to me.

Please post a screen grab of your MeshCAM 3D toolpath window so we can review the settings.

http://www.youtube.com/watch?v=1GlAxiVl2Mc

Spindle speed: 20,000 rpm
XY feed rate: 2,000 mm/min
Z plunge rate: 120 mm/min
Depth per pass: 2.0 mm (roughing)
Stock to leave: 0.5 mm
Tolerance: 0.025 mm
Stepover/stepdown: 1.2 mm (finishing)
Cutter: 5 mm two flute solid carbide slot drills (flat end for roughing, ball nose for finishing)
Material: Khaya (African Mahogany) tonewood neck blank (84.5 x 800 x 40.6 mm)
Spindle: StoneyCNC small industrial quality spindle
Machine: Stepcraft 2/840

Doug

Image
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STEPCRAFT 2/840 CNC machine with 4th axis, TurboCAD V19.2 Pro Platinum, MeshCAM, GWizard feeds & speeds calculator, UCCNC. Hobby use: guitar building (luthiery).
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Re: Poor quality finishing

Postby larynx » Sat May 06, 2017 4:25 pm

Yes, pictures make a difference.

Too reiterate; see these $3.00 with knots rough cedar lumber triple laminated [glued by me] in order to get the width I required, cheapies run to see a prototype base shape and neck contour at not max quality. They are a better finish than the photos depict - because the wood has cracks, knots and pits that the camera exaggerates. If this was quality, sanding is very, very slight. If tighter tolerances I stated are used, then no sanding is required before finish.

Doug - perhaps - unless it suits your needs, a little tighter would help you out too. Last three photos are an earlier cut - at tighter tolerances, NO sanding, just a prefinish coat after fingerboard install, tuners drilled, then would be mated to body, cap placed and then 1500 sand, final & polish.

Unfortunately, this neck will never be used - I dropped it and dented it while taking these pictures! Oh well......I guess I never intended to use it anyway that's why it is sitting around - cause I changed my heels. It was cut from a one piece spanish cedar blank.

The last pic is outside in the sun.
Attachments
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I am not aligned with nor do I have any relationship with MeshCAM or its staff other than being a user [that sounds a little like I have a dependency problem]
larynx
 
Posts: 69
Joined: Thu Oct 29, 2015 2:56 am
Location: East Central Florida


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