The Learning Curve

[Tiercel 6,986]

This post is about my quest to make a HDPE netting needle, warts and all.

 

I decided after seeing some youtube video's and some of the results of catapults made out of HDPE that I could possibly make the Norwegian style needles that I make out of wood out of HDPE.

 

I had a water carrier that was made out of HDPE so there seemed plenty of raw material to work with. The object of the exercise is to turn the water carrier into a functioning facsimile of the Norwegian needle that does not give way after repeated stresses through knitting nets. Or being stood on.

 

 

Having never worked with HDPE before it is going to be a learning curve. I do have reservations as to whether the jaws of the needle will work as they should, but that is a long way off yet.

 

After looking at some youtube video's I set about making my first mould for the HDPE.

 

 

Basically I made the mould around 2mm larger on each side of the blank than I wanted. I know now that it is not enough. The next problem I had was to know how much HDPE to melt to put in the mould. The only way I could think of was to make a blank and weigh it, then melt the corresponding amount of HDPE chips to get the size I wanted.

 

The first blank I made was too small and weighed in at 113g.

 

 

I had also noticed that there were deep lines in the first blank, to my eyes I thought it was due to the HDPE not being hot enough or the mould was too cold therefore causing the HDPE to cool too quick before I could get enough force on with the clamps.

 

 

So I increased the next one to 130g and that was too much HDPE and it extruded out of the top of the mould. I also warmed the mould and increased the temperature that I melted the HDPE on. All that done was brown the HDPE, the lines were still present.

 

 

So I now have to make a new mould of a suitable size so that when the blank is worked on it will not show the lines and bulges, hopefully?

 

So thats how far I have got with this new project I will keep it updated as I progress.

 

TC

Edited January 26, 2015 by tiercel

[moxy 617]

Interesting. Maybe a long shot, but have you considered putting the mould in the oven to slow the cooling process?

 

It may not work too well with the chipboard as the heat will affect the glue but as your only at the early stage it could be worth a try?

[Tiercel 6,986]

Interesting. Maybe a long shot, but have you considered putting the mould in the oven to slow the cooling process?

 

It may not work too well with the chipboard as the heat will affect the glue but as your only at the early stage it could be worth a try?

Believe it or not after heating the mould that was my next step, but, even though I have a huge oven the only clamps I have that can exert enough pressure are too big to fit in there. See what happens with the next mould I make, I have an idea that might just work. The problem with HDPE is that it warps and shrinks as it cools. The good thing about HDPE is that it is always recyclable so even my cock-ups are not a total loss.

 

TC

[moxy 617]

Best of luck

[NELS0N 457]

 

Interesting. Maybe a long shot, but have you considered putting the mould in the oven to slow the cooling process?

 

It may not work too well with the chipboard as the heat will affect the glue but as your only at the early stage it could be worth a try?

Believe it or not after heating the mould that was my next step, but, even though I have a huge oven the only clamps I have that can exert enough pressure are too big to fit in there. See what happens with the next mould I make, I have an idea that might just work. The problem with HDPE is that it warps and shrinks as it cools. The good thing about HDPE is that it is always recyclable so even my cock-ups are not a total loss.

 

TC

 

Could you make the mould out of steel to retain heat better?? or just make a bigger mould and cut off the rough parts.

[Tiercel 6,986]

Best of luck

Thanks I think I will need it. But as you say, to me it is interesting, even if nothing comes of it I will have learned a lot.

 

TC

[Tiercel 6,986]

 

Could you make the mould out of steel to retain heat better?? or just make a bigger mould and cut off the rough parts.

 

 

 

 

Les my next step is along the lines of making the mould bigger. As I stated there really is no waste with HDPE as it all can be recycled. My biggest problem is the wife, I have to do it when she is out, she would flip if she found out I was using the halogen oven to melt plastics in.

 

TC

 

[GruffaloGriff 1,852]

Very interesting, keep postin your progress. Have you tried melting it in a pan of cooking oil on a hob? Just wonder if more heat would make it bind together better?

[Tiercel 6,986]

Very interesting, keep postin your progress. Have you tried melting it in a pan of cooking oil on a hob? Just wonder if more heat would make it bind together better?

I had read about it, the American use Canola oil to melt theirs but it does trap oil in the HDPE so for that reason alone I decided not to try it. Although it has the advantage of giving heat all around the HDPE not just one side of it.

 

http://www.instructables.com/id/Making-Blocks-out-of-HDPE-milk-jugs/

 

TC

[riohog 5,621]

i know nothing about this stuff does it polish when finished ,or does it stay a matt finish?

[Tiercel 6,986]

i know nothing about this stuff does it polish when finished ,or does it stay a matt finish?

Hav'nt a clue, I think it will take some polishing, but how good the finish will be is anyone's guess.

 

TC

[riohog 5,621]

just done a search on the stuff aparently its a mare to work and get some sort of finish on it ,and it cant be bonded with glues or apoxy so its no use to me for knife handles shame its tuff stuff

[air gun ant 1,666]

Is this stuff usually injection moulded or "roto molded" do you no?

[Tiercel 6,986]

Is this stuff usually injection moulded or "roto molded" do you no?

I should imagine injection but I don't really know.

 

TC

[Tiercel 6,986]

Right an update,

 

I tried another blank this week I had the quantity right but as it cooled it shrank and warped. So before I do a new jig that can be tensioned on two side I will try and machine the blanks I have to see if the nose of the needle will be strong enough.

 

TC