cnc profiling core incl sidewalls, trouble sw ripping off

[andi]

hi everyone,
haven't contributed much until now, my bad..been busy sortin out all that devlish little details ..maybe this pic of my press will get me even, giving someone some ideas;)...... there's still some little things to do but it works and resists 8bars with a factor of safety of 1.5 (not the mdf, not the aluminium cattrack)
not sure how to insert pics though....

at the moment i am tryin' to figure out how to prevent the abs sidewalls from ripping off the core during profiling with my cnc. this happened the third time now, always in the thinner area towards the nose and tail, centre is ok.




sidwalls sandeds and flamed, used standard epoxy from sicomin and quick clamps, worked well.. cnc setup is vakuum holddown through mdf, works nicely as long as the core ist flat.

sorry was too pissed off to cklean up.

first try i have been using a 20mm router bit to do it all in one hit....next time tried a 6mm dwncut and profiled just the sidewalls, same result.
headmonkey seems to first route a recess glue them in and then profile
http://www.happymonkeysnowboards.com/Mo ... utout2.JPG
i had hoped there was a quicker way. unfortunately my cam software does not allow to change toolpaths so easily, otherwise some changes here might do the trick.

any ideas, any one???

[chrismp]

i think your best bet is to do it the way happy monkey does it...quite a few people have this problem.
i switched to profiling with a planer and pouring my own polyurethane sidewalls.

what are those silvery parts in your press right above and below the molds?

[andi]

Cheers, might have found something in my CAM to make different toolpaths/change the direction so that the router bit des not 'pull' anymore. Lets see. Might try monkey's version, after all it might not be more work to do on the pc.

Silvery bits.. these are vertical aluminium 'sheets', sort of guiderails for the mold.
Done for today it's snowing. World will be better after some powruns tmrrw.

[chrismp]

i tried to go the router bridge route before using the planer and had the exact same problem. even the wood would get pulled up by the router bit and the tips would become too thin.

one more question on your press. whats behind those aluminum sheets? (you might have seen my thread on my new press design...i'm in the process of building a new press and i'm trying to look at as many press designs as possible)

[andi]

I might be wrong but i might have found a solution by making the toolpaths so that the router bit does only move in one direction/clockwise around the core so that the first contact blade of the clockwise turning bit does push the sidewall versus the core/does not pull horizontally.. and starts frm outwards not inwards like my 2nd try... Not sure will try tmrrw.

Try a vakuum holddown using LDF, quite porous. Seal it below and on the sides and remove the harder top layer. You can 'suck' trough it with two strong shopvacs. This should hold the tips of the core as long as its flat enough.
How does your planer system look like?

Behind are just a couple of horizontal mdf sheets.. i had rather let the press cavity be bigger vertically and then adjust by adding/taking out mdf.

[chrismp]

the planer core profiling works like a breeze! here's a thread with a lot of info on that topic: http://www.skibuilders.com/phpBB2/viewtopic.php?t=537

[twizzstyle]

I'm convinced a drum sander is the only way to go. I've never had success with a planer either. On the last two pairs I did, I actually did a few passes on the planer just to start, then did the rest of the profiling on my base grinder with the autofeed. Worked great, I just didn't use any dust collection so it covered my ENTIRE shop in a thick layer of dust. Dumbest thing I've ever done.

Your CNC looks great. I'm about to start building mine in the next couple of weeks, I've been collecting all of the parts over the last few months and polishing up the design.

[chrismp]

i love the drum sanders too, but they wouldn't even scratch my polyurethane sidewalls

i've found the small portable planers to work best for this application. we started out on a huge 32" width planer and that monster ate half our cores! the problem was to hold the core down on the crib. even with double sided tape and hotglue the planer knives ripped the core right off the crib.

now we're using a 13" Delta benchtop model and it works like a charm. we don't even have to attach the core to the crib. a bit of sandpaper does the trick.

[chrismp]

one last question (really!). what size and wall thickness are the hollow tubes you used for your press?

[andi]

Just lost my post..grrrrr....
What do you mean with hollow tubes?
Not sure about all the dims now.
Girders should be something between around 80-120 x 40-60 mm thicknesses around 6mm, bolts ca 20 or 22mm ?? Press dims ca 2200x400mm.
However don't get me wrong here, i certainly would like to help, but if your press dims are different in only one little bit, your loads will be different and my dims might not be strong enough!!!! As an engineer it's a bit of a liability problem and i don't have the time to do all the calcs for you;)

[carnold]

Hi. I have always done exactly what you are suggesting - follow the outer contour of the board towards the centre and climb cut so that the rotation of the cutter is in effect 'pushing' the edges onto the core. I have been using Alphacam to do the toolpaths and when the post processor is working OK I can get the results I want. I usually use a 40mm diameter TOK cutter in a 3 axis CNC and I get good results. I use MDF but skim both sides and seal with sanding sealer the edges and the area beyond the edge of the core/sidwalls. For making a lot of different core shapes or 3d cores a CNC can't be beaten, for lots of the same a planner or drum/widebelt sander is the go. C.

[andi]

thanks carnold.
so you're saying that way you're not having any sw ripping off during profiling? u do it in one hit or a couple of runs till you reach final thickness? quite a big router bit you're using there, i had a 30mm but for some reason (probably quality/sharpness of the bit) it had trouble makin the profiling in one hit, sort of 'burned' the core no matter what rpms/travel speed i used.
now used a 20mm took longer but worked better, apart frm the sw.

by the way, have you seen wolle nyvelt and his aesmo shapes?
http://www.servustv.com/cs/Satellite/Se ... rchResults
may be something for your snowboat project.
cheers mate

[COsurfer]

Let me save you a lot of time. It doesn’t work and it never will! I tried for months to figure out a tool path that wouldn’t rip off the ptex. The problem is the minimal bond at the end of the effective edge. You will never be able to attach is well enough of the vibration to keep from ripping it off. I profile the core and sidewalls separately and then attach with double stick tape. Its only a temp connection until you press.

[MontuckyMadman]

Doh!

[andi]

@montucky: i‘d rather quit and drink duffs? Or do i have to give you a medal before you may share your wisdom?

@cosurfer: thanks, have you tried monkeys system, doin a recess in the core? Actually i‘m using abs and the problem has not really been the epoxy bond but more the wood next to it splintering in the thin part close to the tips. Problem is only there, the thicker middle section works alright..............So i guess you‘re develloping the sidewalls in CAD to have the correct lenght to thickness then profile ca 10-20mm of a whole ptexsheet with the cnc (no similar problems?) then strip the profiled bit of the sheet with a circular saw (no trouble here due to reduced thickness?) and then bond them to the core?

I thought of maybe somehow fastening or glueing the sidewalls to the mdftable temporarily for profiling, has anyone tried this? or maybe fasten a strip of thin wood (not thicker than min thickness of sw) or similar next to the sidewalls on the table to support them during profiling?

had a lazy day yesterday but now back to the workshop to sort this shit out. one more week until the lifts close.