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Discussion Starter · #1 ·
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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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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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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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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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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Discussion Starter · #6 ·
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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Discussion Starter · #7 ·
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
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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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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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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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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Discussion Starter · #12 ·
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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Discussion Starter · #13 ·
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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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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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
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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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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Discussion Starter · #18 ·
Speeds and feeds for 0.75in or 0.50in HDPE sheet

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
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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