Newbie- HDPE OR MDF NEW MACHINE BUILD

[PKAZ]

Hi Guys, after having a lot of encouragement from reading and trying to learn the basics in building a cnc machine I have finally got the courage to go ahead with a build there is a wealth of information on this excellent site and I have not scratched the surface on all of the information that is needed for a build but with time I am sure I will get there
I only have one question that I need some help on and that is has anyone made a machine mostly out of HDPE its more expensive than 1 inch mdf but my main concern is the not quite so nice English weather damp and cold for most of the year I know you can seal mdf but the thought of making it out of something that is not going to absorb water, not rot and should be maintenance free I just want to get it right the first time around but not having no experience in HDPE I though I would ask the experts on this great site I have seen some posts where people have made some rail adjusters out of HDPE so I suppose my question comes down to this.
Would it be better to make most of the machine out of HDPE or MDf and what are the real pros’s and cons of both, thankyou in advance Paul.

[ger21]

First, no one gets it right the first time. You might get it close, but you'll always find things you could have done better.

I've seen some small machines built entirely out of HDPE, and they tend to have a lot of flex. But MDF can flex as well, the key is that you need to design around the materials weaknesses.

I've never use HDPE myself, so really can't comment on it. But my personal preference would be MDF sealed with a low viscosity laminating epoxy, and well painted. You shouldn't have any problems with moisture then.

[PKAZ]

Thanks Gerry,all info is much appreciated it would be intresting as a test to see which has the most deflection on say a piece 600mm long 250 wide 25 mm thick i know alot of working out has to be done to make your design of your buils as ridgid but light as possible and there are countless proven designs of machines that are in operation at the moment. it always inspires me when i look at some of the posts to see how people over come problems and by the look of things i have a serious amount of reading to do ah well you have to start somewhere thanks again Paul

[ger21]

Originally Posted by PKAZ i have a serious ami know alot of working out has to be done to make your design of your buils as ridgid but light as possible

Keep in mind that heavier is usually better than lighter, as a lightweight machine will tend to vibrate more, and a heavier machine will dampen the vibrations better. But at the expense of needing more power to drive it. You'll find that you'll need to make quite a few compromises when you design a machine on a budget.

[CarveOne]

Certain parts of the machine can be made with HDPE and flexing would not be a serious issue. For the parts that are subjected to stress loading, using aluminum or 8020 type aluminum extrusion would probably be a better choice for damp environments.

If aluminum corrosion is a problem in your area then consider if spray painting the exposed aluminum with "epoxy appliance enamel" (Polyurethane spray paint). You would need to mask off any parts of the aluminum that shouldn't be painted.

CarveOne

[PKAZ]

Thanks guys, I see I have a lot to consider be for I take the plunge but I am sure with the advice I am receiving I shall make the right call in the end, in the mean time I had better crack on with some serious reading thanks Paul

[nicanor76]

for a 1st build I'd use cheap MDF first. Once you have things figured out then you'll have a better idea on what material and overall redesign to use on your 2nd build. Somewhat common for people to not bee totally satisfied with the 1st build

I did alot of search here about materials and seems like alot of people still prefer MDF for it's vibration absorbing quality. But you can't really screw MDF together and have to rely on glue and bolts. For my 2nd I'm using all baltic birch with a strengthened boxed design

[Khalid]

Originally Posted by nicanor76 for a 1st build I'd use cheap MDF first. Once you have things figured out then you'll have a better idea on what material and overall redesign to use on your 2nd build. Somewhat common for people to not bee totally satisfied with the 1st build

I am happy with my first built...I am the one who shifted from steel to MDF

[PKAZ]

Hi guys, to throw another spanner in the works I have come across this site in the uk that do all kinds of plastics and there variants the most promising one I can see on there is PVC due to its mechanical hardness I have sent them an email to find out more about it properties it is also cheaper than HDPE but the idea of doing my first build in MDF so I can iron out any problems seems to me at the moment to be the best idea here is the link for the site that does the plastics here in the UK
http://www.directplasticsonline.co.uk/home.php?cat=3700
thanks for your advice everyone, Paul

[gerryv]

A VERY wise decision, and I'm a plastics guy.