Drag Knife Vs 1/64" cutter

[C Gillam]

Shopbotters,
Firstly thank you for this great knowledge source and community of people. Even though this is my first post, I have spent the previous 12 months lurking in existing threads. Using these existing threads, this forum has help with initial setup, correcting beginners mistakes and currently with the help of few members setup of a 4th rotary axis (still on-going).
The reason that I started a new thread is that I cannot find in existing threads a definitive answer to my current problem.
I have a project that requires 30+ 48x96 sheets of 1/32” HDPE to be cut (all sheets are original cuts, no duplicates). The sheets are to build a mold that interlocks to create a large concrete sculpture.
The sheets contain extremely fine detail (0.029” slots), many tight curves that need to be accurate. I have never completed a task as such and had no idea where to begin (well I come here, that was a good start)
After research I have two differing options-
Use a 1/64 + 1/32” cutter- simple no file modification, high risk breaking cutters
Or use a drag knife-
Donek drag knife- Worried about cutting 1/32 slot, accuracy and required file modification
Widgetworks drag knife- Blade failure cutting large quantities of 1/32” HDPE

My question is those who have experience or knowledge in this type of cuts (find attached dwg), what type of cutter/cutting technique, had being successful. Also how would you hold-down material, I currently use double stick tape, would the shopbot pressure foot be easier?

I understand that I have asked many questions, yet may not have explained the issue well. I did not want to write a huge post, if you have questions or information that you would like to share, please PM or post a reply.

Thanks for your time and assistance.


Please dwg cut file in the following link-
https://docs.google.com/open?id=0B0h7U3i5TPfiQXFZeGZFZDFJSUU

[steve_g]

Wow Craig... you've bit off a chunk! I have to say that I have had very little success cutting with even 1/16" bits... breaking them even trying to tighten the collet! If you do try cutting with a tiny bit, maybe a HSS rather than carbide bit would be tougher. Do you know anyone with an industrial water jet or laser? Maybe someone with one of the drag knifes would try cutting a small section if you sent them material and a file...

SG

[C Gillam]

Steve, thanks for the reply, yes it is a big undertaking, I work for a college in the School of Architecture so time (machine hours) is not so much of a factor.

As for Laser cutting, some industrial shops have mentioned that they do not cut plastics as it voids the warranty on the mirror and lens, others low watt
(<100 W) lasers have a small bed size (need 48x 96").

Water jet cutters have a cutting dia. of min of 1/32 which is too large of kerf (this is possible with material modification).

We are still investigating options, we have the shopbot there I was just hoping that we could complete the task in-house.

Here is a link to the project (named- Cast thicket)
Link- http://tex-fab.net/category/compete-applied/

[jhedlund58]

we have a manufacturer in town makes NUDO board... basically very thin pastic they laminate on anything. Not sure drag knife way to go as i just recently purchased one and have not tried yet. the tech at factory told me to laminate the nudo board onto a piece of luan with rubber cement on one side and clamp (i used vacuum press) important only to use one coat of rubber cement on one side as u want to separate later... if u put a coat on each piece before pressing is more permanent. then i used a 1/8 end mill to cut through the nudo board and removed nudo from luan when done... i took off .0625 or 1/16" per pass on .125 end mill... sounds like your cuts are much finer.... most bits u can take diameter off per pass... ie... 1/4 inch bit 1/4 cut.. but smaller the bit... less u can take so i take 1/16 off on 1/8 inch bit...

i retired.... time is no object 2 me

looked at your web-site etc.. am very impressed and best to you and your efforts

this is my experience and hope it helps

[knight_toolworks]

Hold down is going to be the issue. I have cut a fair amount of .03 sintra and it does not like to stay in place. HDPE will be worse. so even with a drag knife depending on part size they may not stay down. A pressure foot may be a must. I also spray the bed and or the piece with spray adhesive and cut. usually only one side is needed when done shave the spoilboard clean.
the 1/32" and 1/64" bits would not be too bad as long as you ramped in well and made sure you have some extra high so the bit does not touch the material early.
Lasers are fine with plastics as long as they don't contain pvc. but some places don't want to do them.

[zeykr]

I think the pressure foot will be necessary, likely in conjunction with vacuum or other hold down to keep the sheet from sliding.

What about using a small engraving V bit to do the cutting. Would be much stronger than a 1/32 or smaller router bit and angle might not be a problem with 1/32 material. Something like an onsrud 37-25 or 37-23.

http://www.onsrud.com/product/Item/m/itemDetail.html?itemId=37-21

[twelchPTM]

I recently didsome sigag using 1/4" colorcore at 1/16"deep witha combination of 1/16",1/32",and1/64" bits. Figuring out your speeds and feed with such tiny bits can be frustrating but it is possible. Harvey tools makes some nice carbide cutters and there speed and feeds chart is a good starting point. You'll brake a couble of bits but patience is key. I started with some cheaper general purpose endmills and saved the better cutters for after I found my settings

[tomwillis]

Craig - I could probably cut this with my laser. I have a 40 watt mounted on the 2nd Z on my bot....48 x 96 table with vac hold down. Although - I've never cut HDPE - I have cut many materials with sharp corners. You do have a file that will need some slight modification. Some areas where it bends around the tight corners - ie down in the lower third (E) tolerances that are 0.0005"....vs the 0.029. I'd be more than happy to try some cutting for you....to see if laser works....then try to find someone local that will fit your needs. Otherwise - shipping completed rolls from New England to TX - probably doesn't make sense. Feel free to PM me.
Tom

[C Gillam]

Thank you all for taking time to reply, I must say that I am surprised, I honestly thought that the drag knife was the go-to cutter for cutting such materials. For those who pointed out errors in some of the keying pieces, thanks it seems that the file needs substantial work; the project is still in trial mode.
I am currently awaiting arrival of some 1/32 up cut bits, one of the v-engraving cutters Ken mentioned and I just ordered a pressure foot (many issues await me in the coming days).
Steve I will look into ramping, I have no experience with this process, but I am sure I can find out (the search bar in this forum comes to mind).
I was also considering using an available larger dia cutter (1/16 or 1/8) to do the majority of the cutting and only leaving the narrow keying for the smaller dia cutters, but hold-down may be an issue.
Thomas thanks for the offer, but logistics I think would be a issue, we have a laser cutter (65w), I just don’t think they would like me to take out the tube and bolt it onto the shopbot gantry.
Thanks the assistance, time to stock up on super 77 and some replacement small cutters)