# Advice for first CNC router for parts machined from HDPE sheets



## vandomme2 (Jun 11, 2012)

1. I need to machine small plastic parts from 24in or 27in wide x 8ft long plastic sheets, mainly in 0.5in and 0.75in thick HDPE (high density polyethylene), but also in wood for cheaper prototypes.
The largest parts will be approx. 9in wide x 24in long. Smaller parts will be like the 3-point handle in the picture below, approx. 8in x 8in.
I will cut the 8-ft long panels in smaller sections to fit on the machine table.
All parts will have contoured inner and outer peripheries, and also several small through-holes and through-ellipses.
I need to use roundover or similar bits/mills to round off the edges on both sides of all parts. Accuracy is not that important as none of the parts will mate with other parts, but as I need to turn the sheet to round off (and maybe also route) the parts on the other side exactly opposite, perfect indexing is needed.

2. I am thinking about a sturdy benchtop, preferably below $8000 total incl software, preferably US made and also with good or very good customer support.
Estimate is to machine approx. 100 prototypes and 1000-1500 production parts per year.

Concerns are : Ease of defining CAD geometry with several splines and small ellipses, dust collection, vacuum- or clamp part hold-down system, smoothness of routed sides.

I will take a look at TechnoRouters, ShopBot, CAMaster and Probotix but am open to all recommendations. Any advice is welcome!
Paul


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## 4DThinker (Feb 16, 2014)

If you want to stay under 8k then I have to recommend Probotix.com. I own a meteor CNC from them as well as overlook 2 other CNCs from them where I work. Several of the visitors here also own CNCs from Probotix. They sell models with cutting areas ranging from 13 x 20 up to 37 x 50. All under $5k. You can use a router or add a spindle to use. The machines all come assembled and include the controller and PC (running LinuxCNC) just waiting to have all the cables plugged in before you can start using them. The bed is MDF but you can have them add a grid of threaded inserts or come up with your own way to clamp down work.

For software I recommend VCarve pro from vectric.com. The latest version lets you set up and preview 2-sided jobs in the same file. They have several instruction videos online. You can also download a free demo version to try out before you buy. 

4D


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## honesttjohn (Feb 17, 2015)

Plus one what 4D said. But get Aspire of you can.

I have a Probotix Nebula. And aside from figuring out what kind of bed and clamping system is best, it's the cat's banana. Plug and play, ready to go from the crate with whatever software you decide to use. My choice is something from Vectric.

And the support is great. They are located in the Florida panhandle and you can actually talk to the owner or the person who built the machine. They will make everything right and stand behind their product.

HJ


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## Gundawg (Oct 13, 2017)

I think you need a bigger budget and a sturdier machine than a bolt together extrusion machine for what you have in mind and the budget you have set. The Shopbot you mention will run more than your budget when you add a spindle. Getting good edge finish with a hand router as your cutting spindle will not be ideal for HDPE in .5" & .75" thickness and turning out 1000 to 1500 parts. If you are going to make money at this buy a proper machine to do the job. 

I machine HDPE for a living and started with a Shop Bot PRS standard machine I would consider that a bare minimum and it is much more robust than the probotix machines. 

Wood working is not the same as cutting plastic and hobby use is not the same as production use.

As far as round over on the edges it is easier done on a manual machine as a secondary operation. The reason for this is the plastic sheets vary in thickness so your round over will vary even in the same sheet that is why it works better in a manual router with a bearing guide I have a 3.25 HP Porter Cable router mounted in a router table with a fence I round over all the plastic parts after they come off the CNC this gives consistent edge round over. I have seen sheets of HDPE range .010" in the same sheet if the cutter is passing at the same height and you have this variance it will be very obvious but won't be noticeable cut manually with a bearing guide.

I am not trying to put down anyone's machine but unlike wood you can't just sand a rough edge in plastic like you can in wood. Plastic cuts different than wood.

If I were to cut that part in your picture it would be held by vacuum and cut to a .050" skin then trimmed out with a laminate trimmer and rounded over with a manual router mounted in a table with a bearing guide. If you get to the point of getting the machine I can give you some recommendations on cutters with speeds and feeds to get you started

Mike


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## BalloonEngineer (Mar 27, 2009)

I agree with @Gundawg about doing the round over on a router table with a bearing guided bit. 

Save the $2000 that Aspire would cost. That shape is easily done with free software like ArtCAM Free (equivalent to Vectric’s $200 cut2d) or Fusion 360. While it may be drawn with splines or ellipses (which both programs I listed can handle), there is no gcode for a spline or ellipse, so your CAM program will approximate those curves using arcs and short line segments. Again, both of the programs will do your CAM (generate toolpaths) for you. 

Aspire is a great program, but is overkill for parts such as these. Spend the money on a heavier duty CNC router. While vacuum hold down is very nice, if you must, the parts can be clamped down.


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## vandomme2 (Jun 11, 2012)

BalloonEngineer said:


> I agree with @Gundawg about doing the round over on a router table with a bearing guided bit.
> 
> Save the $2000 that Aspire would cost. That shape is easily done with free software like ArtCAM Free (equivalent to Vectric’s $200 cut2d) or Fusion 360. While it may be drawn with splines or ellipses (which both programs I listed can handle), there is no gcode for a spline or ellipse, so your CAM program will approximate those curves using arcs and short line segments. Again, both of the programs will do your CAM (generate toolpaths) for you.
> 
> Aspire is a great program, but is overkill for parts such as these. Spend the money on a heavier duty CNC router. While vacuum hold down is very nice, if you must, the parts can be clamped down.


Thanks for your response! Can the chord height tolerance be controlled for splines, ellipses and radial arcs, e.g. is the approximation fine enough? The sides of the parts must be very smooth to the touch and also visually otherwise it feels and looks bad.


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## vandomme2 (Jun 11, 2012)

Gundawg said:


> I think you need a bigger budget and a sturdier machine than a bolt together extrusion machine for what you have in mind and the budget you have set. The Shopbot you mention will run more than your budget when you add a spindle. Getting good edge finish with a hand router as your cutting spindle will not be ideal for HDPE in .5" & .75" thickness and turning out 1000 to 1500 parts. If you are going to make money at this buy a proper machine to do the job.
> 
> I machine HDPE for a living and started with a Shop Bot PRS standard machine I would consider that a bare minimum and it is much more robust than the probotix machines.
> 
> ...


Thanks for your reply. Yes, I have done prototypes in hardwood, plywood and this HDPE, including rounding off of the edges. And yes, sanding is a no-no for HDPE production parts, it never improves the product. I have sanded plastic prototypes but it's always very visible. The shown handle parts are currently machined on a large Biesse production machine in 27x96in HDPE sheets with some thin skin left at the bottom so I can transport the whole sheets home from the manufacturer and then do the roundoffs manually on a benchtop router the way you suggested. All side surfaces come out really very smooth. I was aware the thickness of the sheet may vary as some of the parts nearly fall out of the sheet when handling the sheet while others stay in. I take your advice that I should do the edges again manually. A handrouter as the cutting spindle will not give me smooth arc surfaces? Can you explain why (cutter speeds/feeds)? The Shop Bot PRS Standard, with spindle, would work for me?


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## BalloonEngineer (Mar 27, 2009)

Yes, generally in the software you can assign a tolerance of how closely the spline is approximated. You will probably need to experiment to find what looks best. Tight tolerance leads to shorter line segments, looser allows for longer ones. There are also settings related to constant velocity vs. exact stop which come into play (may have other descriptions based on the particular CNC controller in use). Generally, true arcs come out smoother than curves made from line segments. @Gundawg may be able to provide advice, as it sounds like he has much more experience with the material, and production routing of it in particular. 

Some type of buffing or polishing operation may be necessary for the best finish, but the right bits, speeds and feeds will make a huge difference in the quality of cut. 

Richard


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## Scottart (Jan 8, 2015)

You live in the Seattle area. it would be a great investment of time to go visit the CNC Router parts folks right in your neighborhood. I have a 48 x 96 pro version, and love it. highly accurate and great support. Some assembly required, but a good way to get more for you dollar and an excellent local support team..


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## 4DThinker (Feb 16, 2014)

If your parts are relatively small, then the best investment would be many machines just large enough to cut one or a few rather than one large machine. For example, The V90 MK2 from probotix has a hardware limited feed speed of 300 inches per minute. Their larger machines are all limited to 200ipm. V90 = 1.5x potential efficiency cutting the same parts out. The more routers you have running at the same time the more parts you can cut at once. 5 MK2s would cost you 3K each, or possibly less if bought all at once. One 4x8 CNC would likely cost you 15k or more, and only be able to make one part at a time. Even if you can lay out several dozen on one sheet, the single router head can only cut one at a time. You would get 5x the production in the same time, and also be able to mix up what you are producing for best efficiency for the current demand. 

Probotix has also made custom machines with multiple heads so one machine can make several of the same part in the same time. If you have a specific production need they will be happy to build and configure one or more CNCs to maximize your efficiency. 

4D


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## Gundawg (Oct 13, 2017)

If you live in the Seattle area I am 2 hours South in Ridgefield, WA come for a visit when I am machining plastic if you like. I buy Starboard which is a Marine grade HDPE in 54" x 96" sheets it is nice to machine a bunch of parts from one sheet.


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## vandomme2 (Jun 11, 2012)

Thanks for the great video and also the invite! I live 30 miles east of Seattle. I have watched similar but simpler cutting of the 3-point handles by the Biesse CNC machine of my manufacturer several times. Your video is unusual in that it shows a variety of different parts from the same sheet. I use half sheets (27x96) of King Starboard as half sheets are easier to handle by my manufacturer (and esp. by me when ready), although it costs me a little as the nesting in 54x96 sheets could probably give me more than 2x36=72 parts.


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## vandomme2 (Jun 11, 2012)

Thanks. I like your idea of smaller machines. However quick production is not needed as I sell maybe 1-4 parts a day online and I can always make a month-worth of inventory (or more) ahead of time. 

However your idea is forcing me to think more/define better what I want to do with the CNC machine. Thinking out "loud":
1. Develop one-piece small parts (in wood, then HDPE or other similar plastic) of my own design that are unique, e.g. that nobody else sells
2. To develop the part I may need to step through 20 - 50 prototypes before getting to acceptable geometry, look-and-feel, functionality
3. Because of the curves, splines, ellipses, holes in each prototype I don't want to do template routing as making each template would be too hard and timeconsuming
4. After the part is developed to the production shape, I want to machine a small inventory of production parts and sell them online on Amazon, likely in onesies, twosies, threesies (hopefully more) per order, maybe 1-4 per day, as needed.

This all means I can probably live with 1 small machine that can at least do my biggest part which may be max 30in long by 10in wide. Now I don't know if such a small machine would be robust and reliable enough to do e.g. up to 1000 production parts in one year, which would be roughly 3 per day in less than 1 hour (time estimated esp. needed for the holes and ellipses). The Biesse prodution machine machines 36 (nested) 3-point handles in a 27x96in sheet in roughly 1 hour, most of that time is spent on the 3 small elliptical holes (36 x 3 holes).

What I don't like about this is that I need to cut up every sheet in many small pieces or ask the supplier to do that, each piece large enough to hold/clamp down and maybe machine 1 or 2 parts out of it. I may waste a lot of material that way and also can't utilize nesting very much (I think).
Any comments/corrections would be appreciated!
Thanks,
Paul


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## 4DThinker (Feb 16, 2014)

One option would be to make a torsion box vacuum table to drop into the frame of the CNC bed. For whatever part you are producing add some quick alignment jigging so when one piece is done all you have to do is drop in the next piece and type R (for RUN) in linuxCNC. When ordering your sheets figure out the best rectangular size to maximize yield and have them pre-cut to that size, or cut them to that size yourself. 

If there are any other steps your parts need to have done after being CNC cut the best time to do those things is when the CNC is cutting the next batch.


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## Scottart (Jan 8, 2015)

vandomme2 said:


> Thanks. I like your idea of smaller machines. However quick production is not needed as I sell maybe 1-4 parts a day online and I can always make a month-worth of inventory (or more) ahead of time.
> 
> However your idea is forcing me to think more/define better what I want to do with the CNC machine. Thinking out "loud":
> 1. Develop one-piece small parts (in wood, then HDPE or other similar plastic) of my own design that are unique, e.g. that nobody else sells
> ...


A 24 x 48 " machine would allow you to feed a full 96" sheet through the table areas 24" at a time while avoiding cutting the full sheet. CNCRTPS sells a 24" x 48" machine that is expandable, should your needs in the future change. Aspire allows you to nest than feed sheets through like this in a process called Tiling. Using tiling and nesting would make for maximum sheet usage with a smaller foot print machine. I carved a set of 72" diameter, 3D wood signs on a 24" x 24" CNC machine using the tiling tool.


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## honesttjohn (Feb 17, 2015)

He did ---- I saw it.


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## RainMan 2.0 (May 6, 2014)

vandomme2 said:


> Thanks for the great video and also the invite! I live 30 miles east of Seattle. I have watched similar but simpler cutting of the 3-point handles by the Biesse CNC machine of my manufacturer several times. Your video is unusual in that it shows a variety of different parts from the same sheet. I use half sheets (27x96) of King Starboard as half sheets are easier to handle by my manufacturer (and esp. by me when ready), although it costs me a little as the nesting in 54x96 sheets could probably give me more than 2x36=72 parts.


Seeing as you live very close to CNCrouterparts, I’d drop by for a tour . There located on the east side of Seattle.
As Scott mentions , there expandable . I’m going to purchase there 4x4 Pro model , and then if I find I can conjure up more room , expand to there 4/8 size


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## vandomme2 (Jun 11, 2012)

*Speeds and feeds for 0.75in or 0.50in HDPE sheet*



Gundawg said:


> I think you need a bigger budget and a sturdier machine than a bolt together extrusion machine for what you have in mind and the budget you have set. The Shopbot you mention will run more than your budget when you add a spindle. Getting good edge finish with a hand router as your cutting spindle will not be ideal for HDPE in .5" & .75" thickness and turning out 1000 to 1500 parts. If you are going to make money at this buy a proper machine to do the job.
> 
> I machine HDPE for a living and started with a Shop Bot PRS standard machine I would consider that a bare minimum and it is much more robust than the probotix machines.
> 
> ...


Hi Gundawg,
My Probotix Nebula machine with 2.2kW spindle will arrive this week. Can you give me your recommendation on what cutters to use, and speeds and feeds to machine 8x8in or 2x24 curved or other small parts from 0.50in or 0.75in HDPE (King Starboard) sheets. It's important that the sides of the parts come out smooth, visibly and to the touch. It will be greatly appreciated! Thanks, Paul


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## honesttjohn (Feb 17, 2015)

Congrats on the Nebula!!!

Hope you got the cross members for support of the bed.


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## vandomme2 (Jun 11, 2012)

honesttjohn said:


> Congrats on the Nebula!!!
> 
> Hope you got the cross members for support of the bed.


Don't know, are the cross members part of the stand? I have the split board with the rotary option.


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## honesttjohn (Feb 17, 2015)

You'll see when you get it. The MDF bed that comes with it will sag if not supported. I took mine off and put 80/20 extrusions with t-slots, and then put my spoilboard on top of it. That's one of the things Probotix does that I didn't like.


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## MT Stringer (Aug 15, 2012)

honesttjohn said:


> Congrats on the Nebula!!!
> 
> Hope you got the cross members for support of the bed.


+1 What John said.

Just thinking out loud. If you have a mdf spoil board...

Create some mounting holes in your files for each different file. That way, you can run that gcode first and mark by drilling a small hole for mounting screws. Then you can get on with your carving. The plastic can be securely screwed to the spoil board out in the middle area, and in places where your parts aren't! :surprise::grin: You could even create a pocket and then drill the center of it so pocket screws can be fastened to securely hold the work piece. And nothing would be sticking up where it might get hit by the spinning bit.

Just a thought. Good luck with the new machine.
Mike


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## vandomme2 (Jun 11, 2012)

*Cutters for 0.75in thick HDPE sheet*

@Gundawg (and others);
My Probotix Nebula machine *with 2.2kW spindle *arrived but did not have the 8-cutter starter set in it. Can you give me your recommendation on what cutters to use, and speeds and feeds to machine 8x8in or 2x24 curved or other small parts from 0.50in or 0.75in HDPE (King Starboard) or similar plastic sheets. It's important that the sides of the parts come out smooth, both visibly and to the touch. I may need low feedrates for the 3 small elliptical holes in the 3-dog handle/triangle. It will be greatly appreciated! Thanks, Paul


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## BalloonEngineer (Mar 27, 2009)

This is something you will need to determine on your machine. This can be the hardest part of cnc usage to learn.

I will recommend you start with a solid carbide 1/4 inch diameter up cut spiral bit. A supplier like Onsrud may be able to provide a recommendation for your specific material, their site also has some excellent recommendations for feeds and speeds, but these are generally applicable to industrial type machines (like theirs). On your Probotix machine, you may find completely different ones work better.

You will probably need to use several step downs to cut completely through the material. Try leaving a few thousandths of material for a full depth cleanup pass. If you don’t understand these terms you will need to read up on CAM processes or ask.

A good process to determine feeds and speeds is to use the zig zag technique recommended by PreciseBits (Tinker and Tinker):

Sweetspot G-code: Zig-Zag Pattern

I recommend you study this code until you understand it, and can modify it. Since your material is very consistent, a few trials and carefully examining the results will pay off. Look carefully, is the cut better on the climb side or conventional side? What feed rate works best? In general you want “chips” not dust. If your getting dust your going too slow (a common beginner mistake!). Carefully feel the shavings - they should be warm, the bit should not be hot (wait til the bit stops and is safe!). 

I do not have experience with your material, but these steps are of general application.


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## 4DThinker (Feb 16, 2014)

Vectrics products, VCarve and Aspire, have a feature in their profile toolpath to have a last pass small stepover so the spiral bit can trim the edge to your final dimension in one step. That's the best way to end up with a clean vertical edge. Their lower end cut2D may have that feature as well, but I don't own it to verify.


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## MT Stringer (Aug 15, 2012)

4DThinker said:


> Vectrics products, VCarve and Aspire, have a feature in their profile toolpath to have a *last pass small stepover so the spiral bit can trim the edge to your final dimension in one step.* That's the best way to end up with a clean vertical edge. Their lower end cut2D may have that feature as well, but I don't own it to verify.


I don't see a "Separate last pass" with an "allowance setting" on Cut2D Desktop that I have.


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## 4DThinker (Feb 16, 2014)

MT Stringer said:


> I don't see a "Separate last pass" with an "allowance setting" on Cut2D Desktop that I have.


I downloaded their cut2D Pro version trial and it has "Do Separate Last Pass" option on the 2D profile toolpath. Not sure about the desktop version though.


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## vandomme2 (Jun 11, 2012)

I am studying the Onsrud and PreciseBits websites, lots of good information. As you say, may still need trial and error.
Simple question so far: For machining MDF and soft plastics like HDPE, having the Nebula with 2.2kW spindle, I think cutters with 1/4in shank will be OK, or is there a reason to step up to 3/8 or 1/2in shank size some of the time?

I also got the trial version of VCarve Pro. It looks fairly good but I hate not having direct POINT definitions, I find it quite cumbersome not having POINTS as defined and usable geometry entities.


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## 4DThinker (Feb 16, 2014)

Not sure what you need points for. If you just want to lay out a drilling toolpath all you need is any size of circle centered where you want the bit to drill. Most drawing features let you click where you want to start, then click again where you want to end. Click in the center for circles, then click any distance from the initial click to set the radius of the new circle being drawn. Rectangle click on one corner then drag to the opposite corner to set the size. Pentagons, hexagons, triangles, etc., can be drawn as well. 

Single points don't have a dimension and would be shown with just a single screen pixel, no matter how far you zoomed in. That is why they aren't used. 

4D


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## BalloonEngineer (Mar 27, 2009)

vandomme2 said:


> Simple question so far: For machining MDF and soft plastics like HDPE, having the Nebula with 2.2kW spindle, I think cutters with 1/4in shank will be OK, or is there a reason to step up to 3/8 or 1/2in shank size some of the time?


The larger bits are stronger. On heavy duty machines, this allows faster speeds. A commercial ($100k+) machine could probably cut 3/4 mdf in a single pass at 1200 ipm. This requires the large bit diameters. I see no advantage on typical hobbyist machines for cutting out shapes with larger bit diameters. Of course I use several bits that have 1/2 shanks for other things, and there is no reason not to use them on your spindle..

You may also want to try downloading the ArtCAM Standard trial. Unlike the Vectric trials, it is fully functional for 30 days (you can create g-code for anything you design, not just a few canned samples). There is also ArtCAM Free, which is comparable to Vectric’s Cut2d line, except free!

Of course, for the projects like you showed earlier, Fusion 360 will be all you need and it is free for hobbyists and startups (under $100k per year). You can draw and CAM your part. It handles cleanup passes easily. 

The Vectric products are very good, but not the only options. They are too pricey for me.


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## UglySign (Nov 17, 2015)

BalloonEngineer said:


> ...Fusion 360 will be all you need and it is free for hobbyists and startups (under $100k per year).


Richard, could you link to the Free for Hobbyists & Startups?
All I find is the trial for 30days.

Thanks!


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## BalloonEngineer (Mar 27, 2009)

The free trial is what you download. You can then register for the free license:

https://knowledge.autodesk.com/supp...-or-educational-licensing-for-Fusion-360.html


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## Gundawg (Oct 13, 2017)

vandomme2 said:


> @Gundawg (and others);
> My Probotix Nebula machine *with 2.2kW spindle *arrived but did not have the 8-cutter starter set in it. Can you give me your recommendation on what cutters to use, and speeds and feeds to machine 8x8in or 2x24 curved or other small parts from 0.50in or 0.75in HDPE (King Starboard) or similar plastic sheets. It's important that the sides of the parts come out smooth, both visibly and to the touch. I may need low feedrates for the 3 small elliptical holes in the 3-dog handle/triangle. It will be greatly appreciated! Thanks, Paul


I use Onsrud bits designed for plastic single flute upcut bit 63-762 is an 1/8" with a 1/2" CEL (cutting edge length) , 63-775 is an 1/4" bit with a 3/4" CEL. These bits do a very good job on edge quality but are not great for pocket floors they are much more rough when used for bottom finishing. I run the 1/4" bit at 1.7 IPS & 18000 RPM one diameter for depth of cut Onsrud recommends running faster but when I have it resulted in a poor edge finish. Hold down method and rigidity of machine play a big role in edge finish as much as the bit. The 1/8" bit I run 1" IPS 19000 RPM and 2 diameter depth 1/4".

For pockets that need a smooth floor (they are not mirror smooth) I use a 2 flute upcut bit 66-000 series. I buy 1/4" & 1/2" diameters of this bit. I run the 1/2" bit 2" IPS and 16000 RPM one diameter depth. The 1/4" 1.7 IPS and 14000 RPM one diameter depth.

Now I do not take a cleanup pass when cutting my profiles. I can cut in one pass but edge finish suffers with experimentation I probably could increase my production by cutting in one pass and making a cleanup pass but I don't run my machine 40 hours a week so speed is not that big of a deal I am usually doing other tasks in the shop while the router is running so optimizing my cutting takes a back seat to getting a good edge finish. The material is expensive and what I am doing works so I see no reason to experiment and possibly have to scrap parts. 

I do not cut through the material on my outside profiles I leave a .050" skin and trim them out with a trim router using an Amana 3/16" bearing guide trim bit. These bits have very tiny bearings so buy extra bearing and pay attention when trimming out the parts you will feel when the bearing starts to go out if you don't catch it you will ruin parts. 

I do not drill any holes bigger than 1/8" I have an 1/8" bit with a 60* tip designed for drilling plastic for the few 1/8" pilot holes I drill for #8 screws. I bore all the 3/16" clearance holes with the 1/8" single flute bit mentioned above using a spiral ramp. The reason for this is if you have very many holes to make the scrap will wrap on the bit and create a plastic ball this will ruin the textured finish on the plastic around the hole this is why I bore those holes. You can blow air on a drill bit to clear the swarf but I find boring them works fine and I don't have to baby sit the process.

I have no connection to Onsrud but they are what I use there maybe be better bits I don't know. I have called them on the phone for advice on what bits to run and when I have had issues so they have good customer support and it never hurts to ask an expert when you have a question.

I hold my plastic with a shop built vacuum table of my design with 5 zones that can be turned off to create different holding areas.

This info has cost me a lot of money to learn and I am giving it too you for free Happy New Year.


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## vandomme2 (Jun 11, 2012)

*Sagging spoilboard on Nebula*



honesttjohn said:


> You'll see when you get it. The MDF bed that comes with it will sag if not supported. I took mine off and put 80/20 extrusions with t-slots, and then put my spoilboard on top of it. That's one of the things Probotix does that I didn't like.


 @honesttjohn I have the rotary option so the 0.75in thick spoilboard is only 29x60inches in size and supported on all 4 sides on the machine. It looks pretty solid and flat. What (bad) affects could I experience from sagging? ( if I machine approx. 16 or 18 8x8in dog handles out of a single sheet 27 x 48 0.75in HDPE). Did you add 'cross'members lengthwise and how many? I was thinking maybe it's enough to have one lengthwise support under my 29x60 spoilboard but am not sure.
I appreciate your input!
Thanks,
Paul


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## honesttjohn (Feb 17, 2015)

One lengthwise or 2 cross ways, in my opinion.

Check out Toolstoday.com for Amana bits. Free Shipping and lots of choices.


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## vandomme2 (Jun 11, 2012)

*Spoilboard sagging Nebula*



honesttjohn said:


> One lengthwise or 2 cross ways, in my opinion.
> 
> Check out Toolstoday.com for Amana bits. Free Shipping and lots of choices.


Does spoilboard sagging esp give poor side surface quality, or does it mainly affect my roundover edges I will do later manually with a small benchtop router after I remove the 3-dog handles from the sheet?


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## vandomme2 (Jun 11, 2012)

Gundawg said:


> I use Onsrud bits designed for plastic single flute upcut bit 63-762 is an 1/8" with a 1/2" CEL (cutting edge length) , 63-775 is an 1/4" bit with a 3/4" CEL. These bits do a very good job on edge quality but are not great for pocket floors they are much more rough when used for bottom finishing. I run the 1/4" bit at 1.7 IPS & 18000 RPM one diameter for depth of cut Onsrud recommends running faster but when I have it resulted in a poor edge finish. Hold down method and rigidity of machine play a big role in edge finish as much as the bit. The 1/8" bit I run 1" IPS 19000 RPM and 2 diameter depth 1/4".
> 
> For pockets that need a smooth floor (they are not mirror smooth) I use a 2 flute upcut bit 66-000 series. I buy 1/4" & 1/2" diameters of this bit. I run the 1/2" bit 2" IPS and 16000 RPM one diameter depth. The 1/4" 1.7 IPS and 14000 RPM one diameter depth.
> 
> ...


Thanks for all your free advice! That will get me started and in the right range. Also your advice about drilling is valuable. I had noticed all the wraps and the heat when drilling circular holes in 0.75" HDPE on my bench press, fun to see but a big nuisance. That's why I can better understand why making the 3 small elliptical holes on my handle part take about half of the total cutting time by my manufacturer's heavy Biesse CNC router. He starts in the middle of the hole with a 1/8 bit and makes many many slow passes = molasses till the final pass.

As you stated holddown method and rigidity of the machine is important for edge quality so I am really hoping my Nebula (which is the largest Probotix) is rigid enough to also machine good production parts and not only prototypes. I don't have a vacuum system, maybe I need it in the future.


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## Gundawg (Oct 13, 2017)

vandomme2 said:


> Thanks for all your free advice! That will get me started and in the right range. Also your advice about drilling is valuable. I had noticed all the wraps and the heat when drilling circular holes in 0.75" HDPE on my bench press, fun to see but a big nuisance. That's why I can better understand why making the 3 small elliptical holes on my handle part take about half of the total cutting time by my manufacturer's heavy Biesse CNC router. He starts in the middle of the hole with a 1/8 bit and makes many many slow passes = molasses till the final pass.
> 
> As you stated holddown method and rigidity of the machine is important for edge quality so I am really hoping my Nebula (which is the largest Probotix) is rigid enough to also machine good production parts and not only prototypes. I don't have a vacuum system, maybe I need it in the future.


Vacuum really helps the sheets are not always real flat and the vacuum sucks the sheet flat. My vacuum system only cost me about $400 to build myself and it works great for plastic. I run 2 built in house vacuum motors each draw 7.5 amps @ 240V. I tried screwing sheets down when first started but soon found vacuum it is like going from a hand held router with jigs to a CNC router if you cut sheet goods.


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