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  1. #31
    Rich what a great job. There is a lot on this site about the merits of mdf v ally v steel. Its the old horses for course and if mdf is what you are cutting then it will do you well. And soooo much quicker than my build now into its 9th month.
    The more I know, I know, I know the less. (John Owen)

  2. #32
    While i agree that you are saying your machine works well as it is in mdf and does the job that you want it to do, I'm sure there is more reason behind everyone's arguments to use metal than just do it as that's the only way, fact is mdf bends a lot. Now the only downside I can see to this flex is that your pieces will run out by a certain amount, this is quite obviously within your tolerances so great for you. I think you may get even more play from your 8 x 4 machine but again if your happy with it then super.

    I originally planned to use mdf for my machine but I wouldn't want to make it and it to have play in it, so I've decided on steel box section as I see this as the next step up from mdf/ply

  3. #33
    TrickyCNC's Avatar
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    Quote Originally Posted by wilfy View Post
    While i agree that you are saying your machine works well as it is in mdf and does the job that you want it to do, I'm sure there is more reason behind everyone's arguments to use metal than just do it as that's the only way, fact is mdf bends a lot. Now the only downside I can see to this flex is that your pieces will run out by a certain amount, this is quite obviously within your tolerances so great for you. I think you may get even more play from your 8 x 4 machine but again if your happy with it then super.

    I originally planned to use mdf for my machine but I wouldn't want to make it and it to have play in it, so I've decided on steel box section as I see this as the next step up from mdf/ply

    Sheep :) you know , one bleats, and the others follow.

    there are plenty of other sources of info and forums on the net, with many many working, and accurate, CNC machines made from wood or wood products. Quite a few cutting ally well too.

    oh and - the fact is , steel bends a lot too ;) in fact, a lot more than you would imagine !

    most of the ally builds on here, you will see them being beefed up /boxed / braced ..., and talk of too much flex and twist etc. etc. "oh , you need bigger/thicker sections/thicknes" ... and so on.

    same goes for MDF. It can be made to not bend.

    One of the longest standing moderators on the CNCZONE (Ger21 - he's on here too) has decided to build his new 8x4 machine from .... err ... oh yes ... MDF ! He knows his stuff .

    There is nothing wrong with steel or Ally. Just don't dismiss MDF . or birch ply . or phenolic ply ..... bamboo ply !

    Rich

  4. #34
    calling me a sheep is a little immature,i happen to be able to make my own mind up about things and have read lots of forum posts given here, with lots of very technical workings out, things people didn't have to do as it shouldn't make any difference to their own life other than the happiness of helping others... its not like the advice here is going to make people money.

    as i saw jazz post in another thread which you are also commenting.. in fact it's my thread.. a sheet of 25mm MDF which i have just bought recently cost me something like 26 quid i think and as jazz had said you could buy enough 50mm box section for 26 to build the same size machine.. i have a welder, yes i bought it to help with my cnc machine but over the past few years it's something i've felt i could have done with and i have no problem buying a tool to tap threads where needed.

    so comparing the raw cost of the materials there is no way a 25mm sheet of mdf will produce the same stiff machine that steel box section machine will, thats not me following like a sheep.. thats me not being stupid and realising the difference between steel and bendy mdf.


    for the record i have complemented you on this machine and i think it's great that you have made it work the way you want it to.. i just dont think it's as accurate as it could be, but thankfully the work you do obviously doesnt need this level of accuracy

  5. #35
    TrickyCNC's Avatar
    Location unknown. TrickyCNC Last Activity: Has a total post count of n/a. Referred 6244 members to the community.
    I didn't mean YOU were a sheep - sorry.
    I meant forums like this in general, people tend to post like sheep. If they've read it, it must be true, so they repeat what they have read... and so it goes on. Even though most have never actually tried it themselves.

    I know you complemented my machine, I said thanks :) but then you say it can't be that accurate ! when in fact you have no idea how accurate it is. It's almost as if you are implying that I don't work with any accuracy, which is kind of insulting to me ;)

    My parts come out the correct size, and square, with no noticeable backlash or carving errors when doing small circles or fine engraving.
    That is my test of accuracy.

    I have said I have play in my X bearings, and I know not to have short fast accel's for it not to show up. That is something I will be fixing. but it's nothing to do with the MDF

    We are cutting wood here remember, not aerospace engineering LOL I have 1 thou (imperial) resolution, but you could never measure wood to that degree, as the fibers compress etc.

    Steel is good. I said that (I think) MDF can also be good, don't knock it till you try it, that's all . (I'm not even saying you should try it, just don't dismiss it because you THINK it's bendy ! )

    I don't want to get on the wrong side of anyone here. but text on a screen can make it look like that (both ways) sometimes.

    ! PEACE n HUGS ! n all that and good luck with your build

    Rich

  6. #36
    TrickyCNC's Avatar
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    Thanks MOTOXY :)

  7. #37
    TrickyCNC's Avatar
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    Click image for larger version. 

Name:	T-BoxShelves5.jpg 
Views:	117 
Size:	47.3 KB 
ID:	6876

    Approx a 4 Ft span.
    Bloke weighs around 200Lb
    Metal bar for visual straight edge reference

  8. #38
    Yer but that picture has been photoshopped Richard, that's really a steel beam you have made look like wood lol

  9. #39
    TrickyCNC's Avatar
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    Quote Originally Posted by martin54 View Post
    Yer but that picture has been photoshopped Richard, that's really a steel beam you have made look like wood lol

    LOL !

    it's not my photo, I googled for an example to show that thin sheets of wood can be made to be 'not bendy'.


    Before starting my design, I made a few test torsion boxes with hardboard skins . it's amazing how they work !

    for them to bend, they have to curve. now everyone knows, the outside of a curve, is longer than the inside. So the only way for it to bend, is for the skins to stretch !
    the further apart you keep the skins , the stronger the end result.


    The only problem you have to solve is how to fix parts to each other, so I chose not to use harboard. With MDF, you can use cheap super glue to 'harden' any fixing holes, which greately increases their strength. washers are good for spreading the load too.
    Another trick is to use a rot treatment/wood hardener over the whole part. it's basically liquid plastic, and soaks into the MDF stiffening it and waterproofing it.

    The use of ply instead of MDF, is also a good option, as it takes screw fixings a lot better.

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