CNC Cutting for Dummies

by Red20RC | December 27, 2014 | (7) Posted in How To

CNC cutting is rapidly becoming my drug of choice. The shear beauty of the finished pieces as they come off the machine is addictive. But getting here was a long and windy road...

This artice is the combination of a number of much longer articles posted on my blog at Red20RC. To view them in their full glory you can go to:

To CNC or not to CNC? That is the question.

2014-07-11 13.09.12I’d been thinking about purchasing some sort of equipment to produce high quality custom components for a while. Everyone was raving about the 3D printing revolution and the chaps at Flite Test were pumping out kits from their laser cutters at a rate of knots.

A CNC cutter seemed the obvious choice. I could cut a variety of components from a variety of materials. They are fairly quick and relatively economical to run.

A short DHL shipping later and my CNC3040Z was unpacked and sat on the workbench.

Setup woes…

The first thing I have to say is that the machine is lovely. The quality is excellent and the fit and finish of the parts are really nice. A little bit of assembly is required to attach the stepper motors to the screw drives but that is about all I needed to do.

I was really excited to get started so it was frustrating to say the least that I then went through anything up to a month of fiddling and head-scratching to get the thing running.

bigstock-portrait-of-young-angry-man-52068682There are a number of modern CNC machines that are USB driven but these tend to be higher end kit. Most machines out there seem to be, like mine, driven by a serial connection. If you are considering going down the same route, here are a few things you need to bear in mind:

  • You will need to buy software to create your toolpaths and GCode as well as software to actually “drive” the machine.
  • You will need to be running a 32 bit version of Windows (not sure about Macs).
  • You will need a proper serial port to plug it into (USB to serial adapters don’t work).
  • It won’t run off a laptop, so you’ll need a desktop running all of the above.

Other things you’ll need…

End MillsOf course, if you want to do any serious cutting you are going to need a good stock of router bits. The shape of these change depending on what you want to do with your machine but as I was only interested in cutting out patterns I went looking for an array of end mills.

Sacrifice board

If you are cutting “slots”, that is full thickness cuts to create something like a multirotor plate, than you will need to protect the bed of your machine. A sacrifice board is a level surface, preferably of softer material than what you intend to cut, that can be clamped beneath your workpiece. I’ve tried a number of things but have found either foam board or simple MDF to be the best solution.

Software Choices

2014-10-13 20.46.30There are a number of different bits of software you will need to get your ideas from inside your head and onto your CNC machine. From what I can tell this will include (as a bare minimum):

  • Some sort of design/modelling software to visualize your design on the computer.
  • Some way to build your toolpaths and generate the code to drive the CNC machine.
  • Software that actually “drives” the CNC machine.

I’m still not entirely sure what some of this software does and I’m pretty sure there will be better ways of doing things but I’ll take you at least through how I do it.

3D Modelling and Blueprints

skpI do everything in Sketchup. It used to be Google Sketchup but now it is owned by Trimble (I guess the same mob that make the Gatewing UAV). Yes, I can hear some of you groaning! I know the pros will be using Solidworks, Autocad or other more advanced tools but I know Sketchup and I find it easy enough to use. It also has the benefit that when I am working with others to produce a design, Sketchup is accessible and I can send files around easily.

Once I have a workable design I use the “Flattery” plugin to export my drawings as an .svg drawing. The good thing about using .svg is that all dimensions and vectors are saved perfectly ready for the next step…

Vector Conversion

Adobe_Illustrator_Icon_CS6My toolpath software can only accept certain file formats and I can't go directly from Sketchup to CAM, so I have to convert and clean up the drawing first. Fortunately I run a copy of Adobe Illustrator for work and this is ideal for the job. Opening the .svg file in AI reveals a number of additional hidden vectors so I delete those, increase the line width slightly to 0.1mm. Rotate the shapes how I want to cut them and then save as an .ai format vector image ready for the toolpath creation…

Toolpaths (CAD/CAM)

CUT2DI saw Vectric Cut2d recommended on a YouTube video and took a look at the software. There were more complicated and expensive options (such as their VCarvePro software) but Cut2D seemed to do all of the things I wanted so a short credit card swipe later and it was on my desktop.

The software itself is easy to use. It is actually a simple CAD program in its own right and the interface makes it easy to import and manipulate the .ai files. One thing I did learn was that once the vectors are loaded it is a good idea to select everything and hit ctrl+j to close all the lines and make selecting paths easier.

CNC Motion Control Software

mach3The manual that came with my machine stated that it was designed to work with Mach3 Mill from Newfangled Solutions, so that is what I got. I am pretty sure that I am still not using this software to it’s full potential but it really is a complex bit of kit.

In a nutshell it takes the G-Code from the CAM software and sends it in real-time to the CNC machine through a serial cable. It is this software that tells the motors how many “steps” are in a millimeter and how fast to spin the drill and move the gantry. Everything starts and stops here so it pays to read the manual and at least learn the basics.

Toolpath Time!

The toolpath is where the fun really begins. There is absolutely no way I will be able to tell you how to design toolpaths in one article but I will give you some of the things I have learnt along the way…

The first thing to do when you open your CAM software (I am using Vectric Cut2D remember?) is to tell it the size of the blank plate you will be working with. I generally use either a 250mm x 200mm or 400mm x 200mm blank. You also need to tell the software how thick your material is as well as where “home” is so it has a point to work from.

I always set home to the dead center of the plate as this is easy to find and mark on the blank with a ruler before I clamp it into the machine.

The next thing to do is to actually import your AI drawings and arrange them on the blank.

TIP: Always leave about 10mm clear around the edge of your blank and make sure you keep the corners free for the clamps. (Or you could simply set your material size to 10mm smaller than the real piece).

cut2d

Once all your plates are in place I found that in Cut2D I needed to select everything and then hit CTRL+J to close all the vectors. This means that if I then try to select a plate outline for example it will select the whole thing rather than a single segment.

cut2d-2Toolpaths are created by first selecting everything you want to cut and then choosing a path style from the menu. For this type of cutting I use either drill or profile. Drill is usefull for the smaller holes whilst profile is the path to use for everything else.

Never try to cut a whole design in one toolpath. By breaking it up into different parts it is easier to monitor and check progress as well as use different size end mills for different components.

Once you have created your toolpaths you need to export them to G-Code. You can add more than one toolpath to a G-Code file but I like to keep it simple and save each one separately. The output I use for my machine is “G-Code Arcs (mm) (*.tap)” and to look at is nothing more than thousands of lines of numbers and letters.

Let’s get on with it then…

So, we’ve got our design and we’ve got our toolpaths, now we need to get the thing cut. Here is pretty much how I go about every project…

Preparing the blanks

I think I already mentioned that I use one of two blank sizes. The smaller size is 250mm x 200mm and this fits most miniquad size frames. The larger plate is 250mm x 400mm for the larger frames.

The sheets come from the factory in 500mm x 400mm sheets and I cut them down with a hand-held circular saw with a thin 40 tooth blade. I cut the plates down in this way for a couple of reasons:

  1. My CNC machine isn’t that big so I couldn’t fit a full size sheet on the cutting bed if I wanted to.
  2. It is easier to work with smaller plates and creates less waste if I cut one frame per blank.
  3. Using the thinner materials, larger plates can bow and vibrate causing problems with cut depth and deflection.

The next thing I do is stick the blanks to the sacrifice boards. As most jobs use both 1.5mm and 3mm plates I stick one of each either side of the sacrifice board.

Hang on. You “stick” the blanks to the sacrifice board? (I hear you ask)

10731871_307782739405995_1401339119_nI spent a long time trying to work out how I could cut components without having to have nasty tabs all the way around the edge. In the end I settled on actually fixing the blank plates to the sacrifice board using spray adhesive. The image shows early tests using foam board blanks but I have since moved to MDF blanks as they are both cheaper and stiffer. Here’s what I have learned:

  • Cut a piece of 3mm MDF to the same size as your material blanks
  • Leave the protective coating on your material
  • Spray one side of both the MDF and the material with spray contact adhesive and press together
  • Put cutting material on BOTH sides of the MDF. This reduces waste and also adds a lot of stiffness to the surface to be cut. If you are using two thicknesses of material (e.g. 1.5mm and 3mm) put one of each on your sacrifice board and cut the thinner material first to maximise the stiffness.

The last thing to do once your blanks are stuck is mark the centers by drawing a line from corner to corner over the protective coating.

2014-12-21 17.50.15-1920

Clamping & Setting Up

My machine was supplied with four screw type clamps that can be moved anywhere around the cutting table by way of square nuts that lock into the channels which run full length.

I marked a straight line (with a set square) across the bottom of my table so I had a datum from which to align my boards and then use the screws clamps on each corner. Alignment is important if you are trying to maximise cutting areas and minimise waste as you don’t want your tool to slip off the edge of your material during a cut. I find that by having the second thicker sheet on the back of the sacrifice board I can clamp right on the corners and still not see any bowing in the center.

With the correct end mill securely clamped in the chuck I now manually wind the point into place so that it is on my center mark, just touching the surface of the material. I do have an electronic z-axis setting tool that I could use but I find it just as easy to find the material surface by hand.

A Short Word About Safety

2014-12-21 18.11.57-1920CNC Machines are designed to cut hard materials at speed using very sharp tools. Once the tool bit is in motion it will keep trying to reach is pre-programmed coordinates regardless of whether it is fiberglass, the metal clamps or your child’s fingers that are in the way.

ALWAYS make sure cutting is done in a safe environment, secure from prying eyes and fingers. If you are going to be near the machine during cutting then make sure at a minimum you are wearing eye protection. You need your eyes to fly so don’t risk them!

The jury is still out on just how dangerous carbon fiber dust is but I know for sure that I don’t want to be breathing a lot of it. If you are running a small bench-top machine like me then make sure you keep a filtered vacuum handy and regularly suck up the dust. If you are going to be doing a lot of cutting then maybe even a cabinet with dust extraction would be good idea.

Let’s get on with it then (again)!

Turn on the power to your machine and then move to the computer. The first thing I do is hit the software “Reset” button to make the connection between the computer and CNC machine. Then I zero the three cutting axis – this is REALLY important as not doing this means the software could think your center point and material surface is anywhere! Now I load my G-Code file and I’m ready to cut.

If I am cutting a very full sheet I will sometimes load the final cut (the component outlines) and “jog” the tool bit around the table at a safe height to check the extremities and make sure everything fits and the clamps won’t get hit.

Only when I am 100% sure I am ready do I hit the green “Cycle Start” button and cross my fingers.

Note: Most cutting software can control the spindle speed through the interface. If yours can’t then you will need to manually start the drill before starting the cutting cycle.

After each cut I check everything is okay by vacuuming off the dust and checking the tool has returned to my center mark correctly. If I need to change tools then I find it is safe to switch the machine off and manually raise the drill to change the bit so long as you remember two things:

  1. Only touch the Z-axis. Don’t touch the X or Y otherwise you might knock it out of alignment.
  2. Reset the Z-axis zero in the software so the machine “learns” the surface point for the new bit.

And that’s it really! Just repeat the process until all your cuts are complete and you have a finished set of components.

2014-12-21 18.46.04-1920

Finishing Off

2014-12-21 18.46.30-1920Once your cuts are complete you should be able to tell (after vacuuming) if the cuts have gone all the way through. Now is the time to find out as it is easy to make some changes to the toolpath and repeat a portion of the job whilst the material is still in place and the zeros are set. Finding out once you have taken the plate off the machine is disastrous!

To make sure I actually remove the components from the blank whilst it is still clamped. To do this I get a small flat headed screwdriver and pry the parts loose. With a bit of pressure the glue or protective sheet will give way making it easy for you to lift the component out.

I can then peel off the protective sheets, check the finish and move on to the next job.

At the end of the day I always take some time to vacuum around the work area to get up any stray dust. I also check the set screws on the CNC machine, give it a wipe over and lubricate the moving parts.

THE END!

CNC machining is a bit of an art and once you get the hang of it it is a total addiction. You’ll have some failures and frustrations along the way but they’ll all be forgotten the first time you put a frame you’ve designed and cut together and feel the satisfaction of the components slotting perfectly into place.

Like I said at the start, this is only a brief chunk of the full series of articles so if you are interested in this aspect of the hobby, pour yourself a coffee and have a read over at Red20RC. If nothing else you'll be able to work out if I should have called this "CNC Cutting BY a Dummy"!

DSCN2353-1920

COMMENTS

Grearson on December 27, 2014
Your final Products look great.
A few questions arise:
What did you pay for your CnC (i am going to DiY one, so ied like to compare costs)
And how much dos such an asambled frame with al screws and such cost you (compared to the 20-30 Bucks for such Frames on ebay/Banggood).

Thx and great job =)
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Grearson on December 27, 2014
Oh and do you share your files for the frames? :p
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Red20RC on December 27, 2014
Sadly not for the ones that i sell through Red20RC. There may well be some free download files in the future though.
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Red20RC on December 27, 2014
Thanks for the comment!
The CNC Machine I bought cost me around USD$1200 with shipping from www.cnc-carving.com.

Cost of production depends mostly on the material used but to give you an idea the frame shown in the article costs around $20 in G10, $28 in Carbon Glass and $38 in Carbon Fiber. That said I do use the highest quality materials I can find so they cost a lot and that price doesn't include things like the cutting bits used or of course the time/cost involved.

I don't think you can ever compete with the cheap Chinese frames by cutting at home so my focus is always on custom jobs and quality over anything else.
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KiwiRCFlyer on December 27, 2014
Hey Red,
Thanks for the great article. I'm really enjoying the CF Red220 quad I bought a few months back. Just waiting for the weather in NZ to clear up so I can get my low fast flight going.

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Red20RC on December 27, 2014
That's what I like to hear!
Make sure you post photos or videos somewhere if you can.
I saw the first video of a R220 "in the wild" the other day and I was so excited!
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rick_harriss on December 28, 2014
As a teacher and long time user of CNC machines in education going back to 1995 I think there are a number of things potential users should consider:
1. The machine will make cutting accurately easier BUT it will only be as accurate as the machine itself is. A common problem with light weight DIY machines is a lack of repeatability - This may be because of a light weight construction flexing or other mechanical limitations.
2. The learning curve for the software is fairly steep. A good CAD drawing package that produces the file type your CNC driver needs is by far the best. An area where you may well get what you pay for.
3. A CNC router can waste a lot of material, waste is expensive.
4. The CNC machine will rarely do anything you can't do by hand but a bit slower!
5 The CNC machine is often not very fast and may take hours to cut large complex shapes.
http://woodgears.ca/bandsaw/cnc.html shows a good lesson.
6. Unless your going to use it a lot you may want to work out the cost/unit and compare to making the odd one or 2 by hand over a slight longer time but much cheaper. Using jigs and patterns can reduce hand work time by a lot making the job a lot easier.
7. Of all the CNC machines the Laser cutter is the most versatile BUT at the hobby level it won't cut everything you may want to cut. Machine cost is higher but material waste is lower, speed is generally faster and you don't need to find a way to fix the material so you can cut it.
8. I am not a great fan of 3D printers - at least not at a hobby level, they are slow, not always all that accurate and costly to run. At school we did almost as well cutting slices from Balsa and Plywood and stacking them to make 3D models.
9. Of the none laser CNC options a CNC mill is the most versatile and the router next. You have to need a lot of turning work to make a CNC lathe worthwhile.
10. Good hand skills can be applied anywhere, a little organisation can make repetitive work faster and easier (jigs, cutting several identical parts at once, patterns). I find that printing my CAD drawings at 100% and gluing them to the material allows me to cut most things with my band saw a fast as I like to work.

Just my thoughts - and yes if I could justify the cost I would have a laser cutter in the garage!


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Red20RC on December 28, 2014
Hi Rick,

Thanks for the comment. It's good to have the insight from someone who obviously has a lot more experience in this field than me!

I am happy that I appear to have got lucky in my choice of machine and software as I have so far (apart from some early mistakes) been able to achieve accurate and repeatable results. I am cutting multirotor frames on a maybe semi-professional basis so I need to be able to achieve some level of consistency in my output. This has however required a steep learning-curve and quite a bit of planning to get to where I am now!

I would definitely agree that the CNC machine is a lot slower than I had thought it would be. When I started I had no idea about things like "pass depth" and "feed rate", I just thought you cut the full thickness in one go as fast as you could - don't ask how many end mills I got through working that one out! The good thing is though that this isn't my day-job just yet, I work from home and I have more than one computer. Apart from the occasional input on my part I am now confident to set the machine running and get on with my work (it's cutting a frame as I type this). In my case then the machine is considerably better than cutting by hand as I have other things my hands can be doing!

The waste issue is one that constantly weighs on my mind. I have been trying hard to minimize material waste and have found my slightly odd spray adhesive clamping method also means I can get components much tighter together without fear of components breaking loose during a cut.

I'd like a 3D printer but I just can't see me using it that much. Every component I've seen looks good from a distance but close up you can tell it's been printed. I don't know; Hovership seems to be making a living out of a printed frame and there are plenty of them appear here on Flite Test so there might be something in it.

Same thing on the laser cutter. If I could afford one I would have one!

Cheers,
Mike
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rick_harriss on December 28, 2014
Hi,
Holding down the material is a real problem that changes with the material type in use.
We tried spray adhesive and Double sided tape with some good results but in both cases eventually the sheet at some point came loose , usually when no one was watching and broke the end mill, ruined the material and my day etc.
In the end we found the most reliable hold down was 4 traditional lever action clamps you see on mills and similar machines. We made our own from wood so we could vary the size. A screw in the middle and a bolt/nut at the end to put pressure on the material work great and rarely if ever failed. The fact they were wood allowed the end mill to touch them and not break (usually), they were very cheap and easy to make.

In the school shop we had 3 A2 sized CNC routers, 1 A 1 laser cutter 1 CNC mill and lath combination machine, like most combination tool it did neither job well.

I cut several Carbon chassis for a racing car project we were involved in and found it really mess stuff. How do you extract the dust?

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Red20RC on December 28, 2014
The dust is a pain! I need to make some kind of extractor cabinet but at the moment the answer is "with a filtered vacuum, often"! I usually run over the sheet with a vacuum after each cut is complete the keep the dust down.

I have exactly the same clamps on my little machine and use them to hold down the plate and sacrifice board. The spray adhesive is used to hold the sheet to the sacrifice board. I started using it for two reasons:
1. I clamp the sheets right at the corners and with thin material of 1 or 2mm I was getting bowing so if I set zero the the center then the edges wouldn't be accurate.
2. I hate having to cut away and file down tabs! I found I was having trouble with tabs breaking and coming loose. Also those larger lightening holes had to be tabbed or they would come loose and foul the machine (as you say - when you're not looking is when it normally happens). But getting a file into these holes to remove the tabs is a real pain!
The spray adhesive seems to solve both of these problems by holding with just the right amount of force. Whether it would work on a larger machine though I'm not so sure.

So much to do and so little time!
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tophe75 on December 28, 2014
I have been flying the Hovership (printed by my self on my 3D printer) and I love it.
Of course you spend a lot of time planning the print but once you have the frame down, it will cost you only a couple of dollars to print a new one, and I know it is not as ridged as a carbon fiber frame but it is pretty good and it is fold-able, I love that.

I do all kinds of RC stuff with my printer.

A few examples:
3D printable version of FT's H-Quad (http://www.thingiverse.com/thing:163794)
Control horns (http://www.thingiverse.com/thing:131758)
Taranis radio stand (http://www.thingiverse.com/thing:468910)

I have been looking at building CNC machine and a laser cutter as the step from 3D printer is not that big.

Just my toughs. Best of luck
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Red20RC on December 28, 2014
Thanks for the comment!
3D printing is one of those new technologies that is just going to get better and better. I'll definitely get one eventually but I'll try to hold off for a bit and see what happens.
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vontugboat on January 1, 2015
I would totally disagree on prosumer-level 3D printers. i assembled my first from a kit (a Mendel) over 2 years ago, and have since built 2 more, one from scratch (a Rostock). They generally provide excellent repeatability and the accuracy is about .01mm which is pretty damn good for a hobby-level machine and certainly good enough for anything that doesn't need to be man-rated. :) The landing gear for my Storch and the motor mounts I've printed are strong enough for heavy use, and the RC warship parts see regular incoming BB canon fire without breaking.

@Red2Orc thanks for a good look at a part of fabrication that I haven't played with yet. Based on your experience, I'll probably start saving for a new toy once Christmas is paid off!
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Red20RC on January 1, 2015
Thanks :-)
I think I'm going to be saving for a 3D printer in the near future!

Mike
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jdlowe on January 4, 2015
I have a pussa i3x diy kit and it prints really well, but took over a year to get it printing good, and well over 100 hours spent tuning it out and fixing it. Save the hassle, get the ultimaker 2, best machine that is comming out for a while.
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Red20RC on January 5, 2015
Thanks for the feedback. I had looked at the Ultimaker when I was researching 3D printers before and I must admit I like the look of it. It always seems to get good reviews as well.
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enivid on December 28, 2014
Hey Red,

Can you detail exactly where you define the path of the milling bit? ie. How you tell the CNC to mill either on the exterior of a line or in the interior?

Great article!
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Red20RC on December 28, 2014
Thanks for the comment!

I build all my toolpaths using Vectric Cut2D. It's a CAD/CAM software that does all the hard work for you and generates the G-Code files needed to run my machine.
You select the vector you want to cut and then tell it which tool to use, how deep etc. In the toolpath setting there are options to cut inside, outside or on the line. I always cut inside for the internal slots and holes etc. and outside for the component itself.
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Pumpster on December 30, 2014
Great article Red20.. My winter project is the OX CNC from OpenBuilds.com . It's been a great project so far, they have a very complete build log and parts list for this machine. I just ordered the last of the need to complete this build. I'm really looking forward to getting this machine running.

OX Link
http://www.openbuilds.com/builds/openbuilds-ox-cnc-machine.341/
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Red20RC on December 30, 2014
Thanks :)

Someone I follow on Instagram is also building the OX machine and I took a look. It certainly looks like an interesting project to undertake. I'd be interested to see how they turn out and how they compare cost/performance wise to other machines.

Good luck with your build!
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skelator on March 10, 2015
Nice, I used to have 3020 but the CNC is too loud for my apartment so have to sell it and bought a 3d printer instead, when I move to a my new house definitely going to revisit the CNC/Laser cutting! for now If I needed something cut I have a friend with Shapeoko 2 ready at my disposal :)
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enivid on March 15, 2015
I've been chatting with some of my mecheng friends an alternative SW to get (FREE) 2D toolpaths is CAMBAM, I played with it and I really liked the results! Check it out: http://www.cambam.info

I was able to import Inkscape drawings into it and generate the toolpaths without too much trouble.
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meglund on June 25, 2015
These machines seem to be complicated to set up, so it's always helpful when someone who has figured it out posts instructions. I've used your advice to set up my machine and it seems to have worked very well for me. What kind of mills are you using for your machine and what different things have you found to work the best? http://richardsmicrotool.com/carbideendmills.html
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The-One-Who-Never-Crashes on January 4, 2016
Thank you so much for these fantastic how-to!
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The-One-Who-Never-Crashes on January 4, 2016
this!
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CNC Cutting for Dummies