|
KOSTAS
|
|
|
Group: Forum Members
Posts: 30,
Visits: 244
|
+xUnless I'm looking at your pic really funny you have your job across the bag ???Just run your job along the bag an cut your bag a lot longer Yes you are right , i was a lot stingy with my consumables ... and i learned that in order to save small you spend big . That was exactly what i had in mind , i just finished redesigning my forks (chainstay and seatstay ) and a support rod to hold the legs in place .      Unfortunately i have the chance to work only on weekends , so mid week is desing and print only . I will post again as soon as i have a new result .Thanks for the feedback.
|
|
|
|
|
f1rob
|
|
|
Group: Forum Members
Posts: 237,
Visits: 4.8K
|
Unless I'm looking at your pic really funny you have your job across the bag ???
Just run your job along the bag an cut your bag a lot longer
|
|
|
|
|
f1rob
|
|
|
Group: Forum Members
Posts: 237,
Visits: 4.8K
|
Will be in big trouble if I photograph these !!!!
For example
From the centre of 1 fork end to the other is say 150mm
When you print your fork at the ends in the exact centre of each you print your 6mm hole
You have a plate with 2 6mm studs pr bolts protruding with the centres at 150mm
Push the 2 studs into your printed holes
Your part is held at the right centre during cure
Once at room temp remove plate/studs
|
|
|
|
|
KOSTAS
|
|
|
Group: Forum Members
Posts: 30,
Visits: 244
|
+xDosent matter how big you make your bag or how careful you vac down it will never pull down symmetrically, there will always be resistance from one point or another If your bagging somthing that can move or flex then it will ! Brake drums on the f1 cars are made with lots of printed formers now. What they tend to do is on the open end they print it with 6mm holes You then have a plate with pins on the correct centres that you push into the holes then bag the whole lot up I would be really interested to see any kind of picture if avialiable to have a better understanding , thanks
|
|
|
|
|
KOSTAS
|
|
|
Group: Forum Members
Posts: 30,
Visits: 244
|
Thank all of you so much for your fast and though insight , this is such a good place to be and learn, i spend quite a time here reading  As you may see from my picture i have bought and use a tubular vacuum bag 460 mm wide . Since these consumables need some processing time and are not readily available to the place i live the faster way to get a bigger bag is to slice open the bag i have and connect two pieces .It would be rally easier for me to see a picture of a big bag with wriggles in order to understand how to strategically place my item in the bag.Sorry but i have zero experience .
|
|
|
|
|
f1rob
|
|
|
Group: Forum Members
Posts: 237,
Visits: 4.8K
|
Dosent matter how big you make your bag or how careful you vac down it will never pull down symmetrically, there will always be resistance from one point or another
If your bagging somthing that can move or flex then it will !
Brake drums on the f1 cars are made with lots of printed formers now.
What they tend to do is on the open end they print it with 6mm holes
You then have a plate with pins on the correct centres that you push into the holes then bag the whole lot up
|
|
|
|
|
oekmont
|
|
|
Group: Forum Members
Posts: 550,
Visits: 27K
|
Absolutely. The bar will keep the ends at the right distance. Than you only have to worry about bending the two arms. But this should be less of a problem.
|
|
|
|
|
Steve Broad
|
|
|
Group: Forum Members
Posts: 408,
Visits: 4.1K
|
+xIf you close the print, the're is no force in the core itself when you pull vacuum. The pressure outside the bag is 1 atmosphere, as is the pressure in the core. The pressure between core and bag is zero, and this is why the bag is forced against the core, and the core against the bag with equal strength. An open structure however has to be able to take the forces of the vacuum without collapsing. But this is not you problem. Your part did shrink to this, but this should be immeasurable small for you. Your problem is that you placed the bag flat over the part. The way across your part, following it's contours is longer than the way across the part without following the contours at all. And as the bag was evacuated, and came to a point where it had to move inward to fill in the space, it was already to tight, to slide over your part and compensate the additional length. So the bag had to stretch to get into the corners. And by doing so, it created an equal force, which pulled the arms of your wishbone inwards. And this is why you should never put the bag on without wrinkles. Theoretically not even on a flat sheet. That's a better way of explaining it than mine :-) However, I would still would place a bar of some sort between the ends of the fork as you evacuate.
|
|
|
|
|
oekmont
|
|
|
Group: Forum Members
Posts: 550,
Visits: 27K
|
If you close the print, the're is no force in the core itself when you pull vacuum. The pressure outside the bag is 1 atmosphere, as is the pressure in the core. The pressure between core and bag is zero, and this is why the bag is forced against the core, and the core against the bag with equal strength. An open structure however has to be able to take the forces of the vacuum without collapsing.
But this is not you problem. Your part did shrink to this, but this should be immeasurable small for you. Your problem is that you placed the bag flat over the part. The way across your part, following it's contours is longer than the way across the part without following the contours at all. And as the bag was evacuated, and came to a point where it had to move inward to fill in the space, it was already to tight, to slide over your part and compensate the additional length. So the bag had to stretch to get into the corners. And by doing so, it created an equal force, which pulled the arms of your wishbone inwards.
And this is why you should never put the bag on without wrinkles. Theoretically not even on a flat sheet.
|
|
|
|
|
KOSTAS
|
|
|
Group: Forum Members
Posts: 30,
Visits: 244
|
This issue really bothers me a lot , cause i could not predict it and i could not explain it .After some study i have a theory , i cant say its the cause but might be an explanation. I printed a U shape with thin walls that was not airtight, that means that the vacuum pump pulled air from the inside of the core also.Thus making my mold behave like a bourdons tube  the working principal of many pressure and vacuum gauges .When you apply pressure to the curved tube the tube expands, when you drop the pressure it contracts.Initially i thought that i should print my core airtight so that air from the inside of the mold not to be able to escape under vacuum , but in that case this might bring the opposite result and make the u shape expand this time!! Of course i could print my mold solid but this is my last choice since i s a big waste of printing time and material . i will try first the added support you method you suggested just my thoughts thanks for the feedback anyway
|
|
|
|