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Discussion in 'CNC Mills/Routers' started by Hytech2k, Nov 28, 2014.
This is my journey on building a rack and pinion Ox variant called the F-117 CNC.
With G10 plates very nice, how much more would 6061 stiffen it?
I wish I could answer that, i'm not sure of actual scientific data, i'm more of a trial and error fellow. The G10 is extremely stiff, when you tap them together they sound like glass. Putting pressure on them I can't seem to make them deflect. I think moving to all aluminum will help reduce any chatter and raise cutting speeds.
Modulus of Elasticity of aluminum is 10 (x 10^6) psi
Modulus of Elasticity of G10 is 2.7 (x 10^6) psi lengthwise and 2.4 (x 10^6) psi crosswise
So for similar thicknesses, aluminum would be 3.7 to 4.17 times stiffer. For non similar thicknesses, the G10 would need to be 54.7% thicker than aluminum to have the same stiffness (assuming flexure across the lengthwise direction).
It should also be noted that there is no appreciable difference in stiffness across the different grades of aluminum. 5052, 6063, etc. all flex the same as 6061.
What he said......
Great information Rick
Given the price difference between the two materials after machining costs I like the aluminium with the additional stiffness. But Hytech has also proven that the G10 is up to the job!
It's a funny thing, I was just getting ready to order some material to cut plates out for my store, after shipping costs G10 is equal in cost if not slightly more than 6061.... So I think i'll be offering the plates in CE Phenolic for economy version kits and 6061 for standard kits...
Great info seriously !! I'm glad someone has the science and engineering info !
The Modulus on the CE is 1.6 (x 10^6) so it is a noticeably less stiff than the G10 but it should be fine for small plates. If you are looking for cost reductions, consider 3/16" aluminum plate. It's 56% stiffer than 1/4" G10 and 20-25% less in price than 1/4" 6061. And if you'll recall, the original OX was built with 1/4" G10 so that should give you an indication that 3/16" 6061 should be fine for regular applications.
Both materials should perform about the same.
The reason for the differences in the modulus is because the g10 composite doesn't yield as aluminum or steel. Instead of deforming prior to failure mode (like the metals) the g10 pretty much skips plastic and elastic deformations an goes right into failure. It acts more like a ceramic than a metal or plastic and just breaks instead of stretching first.
Comparing the tension and compression strengths of g10 to aluminum is more straight forward. G10 and 6061 are quite similar. 35 to 45000 psi until failure.
Realistically, I don't think any part of anyones OX plates are going to see the amounts of forces we're talking about here.
Just my two.
Well that's interesting, so it really wouldn't matter then if I cut plates from G10 or 6061 for this particular application for the fact this machine will never be able to approach the limits of the materials. Correct? This matters to me from a machining aspect, G10 mills like butter compared with 6061. Through my supplier the materials are close to being equally comparable in costs. I could probably go with CE Phenolic for those who don't really have an interest in cutting 6061, just woods and plastics save them a bit more on construction costs, even cut down the # of wheels to more like 4 on top and 3 on the bottom... Thanks Joe !
I notice you use Fuchs proximity limit switches on your builds. Can you explain to a newbie why these are better then simple switches. I will be using mach3 software.
I like them because they don't foul with debris, you could cover one with sawdust and it'll still work, plus I use them for homing, limits, and squaring, the repeat ability is excellent. But good Honeywell micro switches will work too, alot of people use them. Mach 3 is easy to setup for any of the switches. The only ones I would shy away from are the optical ones, they do have problems with dust...
Thank you. I ordered some simple waterproof ones just because they were in-expensive and did not have the experience to know why the $150 solution was better!
I can always upgrade in the future, when I start generating dust!
I just wanted to post this info Joe Santarsiero was kind enough to share with me, I really feel that there is alot of useful information there for others wanting to design their own plates and kicking around what materials to go with... I am not an structural engineer or have a good grasp of the science behind stress testing, so I value the information Joe and Rick can provide to those of us not educated enough to understand "Modulus of Elasticity".
"Well that's interesting, so it really wouldn't matter then if I cut plates from G10 or 6061 for this particular application for the fact this machine will never be able to approach the limits of the materials. Correct?"
From a machining aspect and to keep things simple I'll say yes. That is correct.
However it is not that simple Tech. The Al and the g10 have very different characteristics and design must consider these properties. For instance, Al is such a great thermal conductor that it could be beneficial to a system that naturally performs very well, but runs hot motors. In the case of the G10....it is almost opposite. In fact, it's a thermal insulator. One with a hot running system as mentioned may have to install sinks on steppers to accommodate them (zip ties anyone? )).
Another thing to consider is the environment. G10 has the ability to absorb moisture (not well though). If one decides to run a wet system then the question of whether or not certain cutting fluid ingredients will have an immediate or long term impact on integrity is good first question. Though I doubt this is an issue. Any chemical engineers around?
The construction of G10 itself requires attention when designing as well. Because it is a laminate it actually has two different stress strain curves that give it two separate tensile strengths. One is pulling the lamination away from itself perpendicular to the bond and the other is pulling perpendicular to the bond in the direction of the lamination. The latter being as strong as Al and the former being less, but not significant in my eyes for the application. (approx 16%)
This information is important when considering flexing forces, specifically unilateral bending of the floating gantry plates with Y moving cuts (the long way) and bilateral torsion involved on all plates while cutting with X and Y or X,Y,and Z simultaneously. Things that are involved with this machines normal operation.
The reason to consider this: laminated materials require a little more attention to these types of stresses because many of them are naturally more prone to failure when thickness is reduced and such flexure is involved. Mind you, this depends on the bond. The better the bond, the better things get when thickness is reduced (increasing number of lamination's is for another day!).
To better explain. I'm going to present three scenarios. All contain parts made of G10, but the materials construction is different (not an issue with aluminum)
Part is made from a sheet of .500" thick G10 and is cut 1" tall and 4" wide
Part is made from a block of G10 that is 4" in depth and cut 1"wide and .500" tall
Part is the same as part one.
So with these three pieces of imaginary stock we do some tests.
Part one is pulled from each end the long way and proves to be as tough as Al (Pulled along the lamination)
Part two is pulled from each end and it is determined that the G10 is 16% weaker (pulled opposite of the lamination)
Part three we flex between two point on the bottom at opposite edges and at one point in the center on the top.
Part three is unique because we are introducing compression on the top, tension on the bottom, and "most importantly" shear through the middle which is between the tension and compression. Compression is of least concern because it requires the highest amount of force of the three and. Tension is a standard because it is most common mode of failure. Though shear is much more easily identified and calculated, forces required for Shear is the one we are most concerned with because, of the three, shear strength requires the least amount of force to fail most solid materials and is of special interest when a laminated composite is involved such as the case with G10.
With all of these things considered, I'd pay special attention to the thickness left at the pocket for your steppers, keeping the amount of material removed kept to a minimum, change the square corners of the pocket profile left by the mill bit into fillets by using a corner radius cutter (4 flute (let me know if you find anything above!)), and paying good attention to final surface finish overall.
"This matters to me from a machining aspect, G10 mills like butter compared with 6061."
Considering G10 is a glass composite you should plan for significant cutter wear once you enter a production phase. Of course with the proper aluminum designed bits.. tool wear would become less significant when working with.... Aluminum. There aren't really bits available that are specified to work with fiber composites, but there might be some white papers out there that'll help. Maybe considering investing in a good diamond carbide or even diamond coated cutter for production with G10. Those may have a higher upfront cost though. From my personal experience, I'm inclined to point you in the direction of dry tooling used to cut graphite. The reason I say this is because of your report that the G10 appears to cut like butter. I'm also considering that you're cutting with high speed and feeds which would make more sense with the material. If your cutting fine glass you probably want to shock the brittle fibers immediately after giving them a stress concentrator in order to reduce free strands and to increase finish. Graphite responds this way...minus the epoxy! My concern for you is that tool wear will be significant with standard tooling and you'll see this after a small number of parts. Mainly because of the glass. Please report back on this as I tend to retain such info for whatever reason. ...
"I could probably go with CE Phenolic for those who don't really have an interest in cutting 6061"
You could. Just eye up the properties and know what your working with prior to fabrication.
Just glancing at your design.... I tend to focus on the outer wheels of the dual gantry plates. If ones Z went into the work (common) then I think the plates may absorb a torque translation through the gantry beam and would impact the outer wheels from the inner wheel holes to the outer profile of the plates. This is of course considering there isn't a weaker link in between. Without doing the math or beating up a machine intentionally to get the data...it's tough for me to say that this could be of a real concern or even have an effect when considering functionality.
Suggestion, leave some more material between the outer profile and any internal features when using the G10 or phenolic. The positive about the Al in such a case is that deformation would be measurable (and permanent) prior to failure compared to the other two materials.
As far as i'm concerned this build has proven itself, i've cut probably 20 different signs ranging from straight easy v-carve stuff, signs with a good mix of pocketing and 3D, to full on 3 hour per sign 3D cuts !! No issues what so ever.. We even cut some .25 6061 aluminum just for kicks !!! I am in the process of assembling a BOM for this machine now, the plates will be available from me the first week of February. I will be offering them in 6061 aluminum for right now, i'm setting up to anodize now so plate sets in different colors will be available. Here are a few photos of a portion of the signs this machine has cut over the past few days.
I am extremely pleased with this machines performance and it has met and exceeded my expectations. I believe it will fit in great as a primary or secondary machine in a small business production capacity. Over the next few weeks I will be ordering the parts to assemble a vacuum hold down system using 3/4 Phenolic to make "vacuum pucks/jigs" . I think this will be much more cost effective given the type of work i'm currently doing. I really would like to use the bleeder board method, and maybe I will on my large machine if I go to start cutting a lot of sheet goods, but I don't think it's best when some of my signs take up to 5-6 hours nested. That would certainly be hard on vacuum motors and my electric bill. Thanks and stay tuned for revisions on this build !!
If anyone needs proof the evidence is shown above.
Awesome signs, design, engineering and build!
Really great job...
Thank you !!
Great work all around.
Just to second what others have said - Great work & great build.
VERY nice machine, I've learned a lot from your design process!
I'm curious, what are the bits that you use. They look like Amana tapered ball nose, but I'm not sure. Also, where do you get them from?
Love your signs too!
Thanks everyone !! I buy my tapered ballnose bits from either precisebits.com or toolstoday.com. They're expensive but worth it.. My 1/16th bits are ZrN coated Amana bits from toolstoday. I also use CMT v bits I get from Amazon, good quality. And for profile cuts I pretty much always use a 1/4 2+2 compression bit, leaves perfectly clean edges unlike a upcut or downcut, less cleanup... I've compiled a list of companies I buy from, if anyone is interested i'll post it here...
Yes please do!
Yes please, a list of bits, styles and suppliers would be extremely useful.
This is not all inclusive of all the bits I use, just the places I can remember at the moment. I'll probably amend this list a few times. Don't even bother buying bits from Home Depot or Lowes, they don't come close too the quality of these suppliers and priced too high!!
Magnate 2705 Surface Planing ( Bottom Cleaning ) Router Bit - 1-1/2" Cutting Diameter (good for surfacing spoilboard)
Magnate 761 V-Grooving & Carving Router Bits, 60 degree - 60 Degree; 5/8" Cutting Diameter (Good V bit too, I like three flute bits, easier on softwoods, less tear out and fuzzies)
Whiteside Double 1/4" compression bit
Milescraft downcut bit (great for pocketing where texturing will be cut later)
CMT 1/8" downcut (great for smooth bottom pockets)
CMT 858.001.11 60 degree Laser Point Bit (probably the best 60degree bit)
Niagara Cutter N55803 Carbide Square Nose End Mill, Inch, TiAlN Finish, Roughing and Finishing Cut, 30 Degree Helix, 4 Flutes, 3" Overall Length, 0.125" Cutting Diameter, 0.125" Shank Diameter (great for drilling screw holes)
CMT 815.064.11 Solid Carbide V-Grooving Bit, 1/4-Inch Diameter, 1/4-Inch Shank (good for v carve lettering)
(.0625") CARBIDE 2 FLUTE ENDMILLS, DOWNCUT FOR SOFT PLASTIC (work great in wood too plus CHEAP !!)
5pcs Single Blade Aluminium cutting single flute CNC router bits 3.175*3.175*12m (OK bits, cheap !!)
Awesome bits for aluminum but expensive
Solid Carbide CNC 2D and 3D Carving Tapered Ball Nose and Flat Bottom, Zirconium Nitride (ZrN) Coated Up-Cut Router Bits (some of the best i've used so far !!)
Precise Bits (great quality tapered 3D carving bits)
Beckwith Decor Bits (alot of folks say these are the best 3D Tapered bits, I haven't tried them a bit out of my price range)
This is great thanks!
Agree, really great source of information. Trying many brands and types is a costly experience, so this really helps.
I've been where you guys are, I started out buying from HD and Lowes, ummm not good, the only decent bits that lasted were the Bosch but too expensive.. Bits are a big expense for a small business, looking at my bit holder I probably have close to $500 in bits and collets there, they add up quick !! I hope this helps, if anyone needs to know what feeds, speeds, and DOC have worked for me with any of those bit let me know. Breaking a bit hurts...
"Breaking a bit, hurts a bit, for a bit!"
Love this build, do you think it would be rigid enough for a 4x4 cutting area?