[Mavigogun]

I aim to carve some large blocks of HDPE plastic, and am looking for tooling that can reach 7" or more. Are such tools available with a 1/2" shank? The intended AVID CNC employs a 4HP spindle that MIGHT accommodate an ER32 collet receiving 3/4" shank tools.

[Ashley-techprolaser]

First,it is difficult to find 7" tool; secondly, if you need to engrave a depth of 7 inches, you do not necessarily need a very long tool (unless you need to drill), because the cnc router engrave it layer by layer.But if the hole you carve is too narrow for the spindle to go deep, it will be difficult.

[routalot]

I fear that finding tooling may not be your biggest problem.My experience with a few types of plastic suggests that the internal stresses within the slab can lead to rather a lot of distortion when the item is taken from the machine.Anything much larger than a cigarette carton will definitely not be flat on the bottom face when machined to a high proportion of it's depth.Try a sample before going too far down the path.

[Mavigogun]

I appreciate the threat of distortion. The HDPE billets themselves, at about 75lbs, will be annealed, spending almost 2 full days in oven between melt, soak, and cooling. The stock will be actively cooled, as necessary, if heating becomes an issue. The end product will resemble a brick with relief carved into one face- that is, there will always be a large amount of mass backing the carved face, and high aspect ratios will be avoided.

[joeavaerage]

Hi,
HDPE is about the worst machining plastic there is. It forms strings rather than chips, a PITA. I use flood cooling with ALL plastics, and HDPE especially,
its less about cooling but trying to flush away the chips. If you fail to do so the chips get recut and weld themselves into a lump or stick to the tool.

Craig

[Mavigogun]

Without doubt, HDPE has certain demands. My understanding is that string formation may be managed with proper feed and speed, cutting strategy, tooling, and adequate evacuation (air).

Considering the depth of operation, I reckon at least 3/4" diameter carbide tooling will be necessary.

[joeavaerage]

Hi,

My understanding is that string formation may be managed with proper feed and speed, cutting strategy, tooling, and adequate evacuation (air).

Have you actually tried it? I have bits of HDPE, UHMWPE and various Nylons tossing around the workshop......and they never really get used up...they are such a mongrel to machine.
If I'm making a part that needs to be good, I'll go and buy a piece of Acetal or PEEK or PTFE or whatever rather than use the stuff I've already got lying around.
For parts that don't matter too much then I might use my existing stocks of Nylon or HDPE.

Craig

[metalmayhem]

looking for tooling that can reach 7" or more. Are such tools available with a 1/2" shank? .

to answer your question there are a lot of tools available with that reach . htc for one has a 1/2" with an 8" oal . Ideally a downcut would be your best bet but that might be tough to find . I'd check with harvey , they tend to have oddball stuff

[Mavigogun]

Excellent references- the prices for 8" carbide at HTC are great! Much thanks!

[metalmayhem]

they make decent general use carbides and I always find the prices to be good . Mari tool is a good source for htc but I'm not sure if they have the 8" on the site .
You won't have the flute length to match your depth , so it'll be necessary to grind some relief in the shank to avoid rubbing if your using it to profile the pocket walls

[Mavigogun]

For those interested in reaching long into HDPE, I received some experienced feedback over at the Practical Machinist forum, here:

practical machinist (remove the space and stick in the "dot" commerce, 'cuz this site censors the link) /forum/threads/long-tooling-stick-out-for-hdpe.419531/

[routalot]

Hi,



Have you actually tried it? I have bits of HDPE, UHMWPE and various Nylons tossing around the workshop......and they never really get used up...they are such a mongrel to machine.
If I'm making a part that needs to be good, I'll go and buy a piece of Acetal or PEEK or PTFE or whatever rather than use the stuff I've already got lying around.
For parts that don't matter too much then I might use my existing stocks of Nylon or HDPE.

Craig

My experience of 75mm Acetal was that it didn't remain flat with much material removed.Having said that,it was better than UHMWPE or HDPE.I can only imagine what will be in store with a 7 inch slab and it isn't appealing.

[Mavigogun]

Distorting parts is a possibility. What was the history of your stock? Was it annealed? What cooling did you employ? Was the tooling designed for plastic? Did your operations feature high feed rates and significant material removal?

[Mavigogun]

A brief survey of plastic machining services shaping HDPE returned work in MUCH larger dimensions than I propose. Speaking to distortion, technique and capacity seems to be the determiner of practicality and results, not some innate unsurmountable liability of HDPE. Some of the contributing factors include the generally understood need to remove substantive material quickly to avoid heat transfer, with the balance invested in the evacuated chips, air evacuation/cooling, but also tool design, with the geometry of some tooling actually drawing stock toward the tool (bad), or the tool applied with excessive force resulting in reciprocal distortion- sometimes at locations distant from the tool!

[routalot]

Distorting parts is a possibility. What was the history of your stock? Was it annealed? What cooling did you employ? Was the tooling designed for plastic? Did your operations feature high feed rates and significant material removal?

I have only ever machined plastic in the condition it was supplied in.I am curious about the idea of annealing it,where would you suggest I look for more information?

[metalmayhem]

the best approach to any material that relieves itself is to - do the bulk of the machining ops while leaving enough material for finishing , re-clamp lightly as safely possible and do the finish ops . The re-clamping is the important part which lets the material rest .
I've had to use that approach many times with plastics , steels , titanium and even aluminum .

[Mavigogun]

I can point to some general proscriptions gleaned from Google- https://www.boedeker.com/Technical-R...ing-Guidelines -but there's a good deal of ancillary information I discovered along the way that should be kept in mind; monographs on the topic may be found here: https://discord.com/channels/5866767...31703688089620

[joeavaerage]

Hi,
reading is all very well, but why don't you try it?

Your local engineering plastics supplier will have any amount of HDPE offcuts, even if they are not the same size and you can have some for cheap. Grab some carbide tools of similar sizes to your intended
long reach tool and do some cutting. You'll learn in half an hour what you can't read in a week.

Craig

[Mavigogun]

I've sourced post-industrial regrind- it will provide a consistent material for testing. My candidate long reach tooling ranges from $250-$750 USD; I judge consultation a prudent preface- and far less expensive -than uniformed experimentation.

[joeavaerage]

Hi,
which is exactly why I am suggesting a few small pieces of material and a vastly cheaper tool. I would suggest an experiment that would cost less than $100.
Clearly you know more about than I do...good luck to you.

Craig