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  1. #61
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    Aug 2008
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    Quote Originally Posted by Ch4iS View Post
    No worries , I've attached some pictures of the frame to give you a better idea.
    Ok, you have supports at font and back, therefore a midspan support could be easily provided.
    This midspan support will attract more load than side channels.
    Is your framing done by 75SHS members>

    Regards
    Zvon

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  3. #62
    Join Date
    Apr 2011
    Location
    Pakenham, Victoria
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    53
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    350

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    Hi Chris

    I've been watching this one with interest for a while. I'd love to try to do a small one one day. Well done so far mate and thanks for sharing.

    Just a quick question. Can you get that sort of paint finish with aerosol cans or did you use a spray gun?

    Danny

  4. #63
    Join Date
    Feb 2008
    Location
    Australia
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    988

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    Quote Originally Posted by zvon View Post
    Ok, you have supports at font and back, therefore a midspan support could be easily provided.
    This midspan support will attract more load than side channels.
    Is your framing done by 75SHS members>

    Regards
    Zvon
    Yea it's all 75x75x2.5mm. I'm thinking of using 50x50x5mm RHS for the support beam, possibly adding two, sufficient or beef it up? will need to still work out brackets ect. but it'll be butted up against the PFC so I can bolt angle pieces to it.


    Quote Originally Posted by danny.s View Post
    Hi Chris

    I've been watching this one with interest for a while. I'd love to try to do a small one one day. Well done so far mate and thanks for sharing.

    Just a quick question. Can you get that sort of paint finish with aerosol cans or did you use a spray gun?

    Danny
    Thanks I used a spray gun only because it's cheaper to run, $50 for 4 litres from protec, the cans just don't seem to go very far, I find good quality cans like the rust guard from bunnings leave a better finish than with my spray gun, but they're about $14 a can. My HVLP spray gun is only a $20 internet special.

  5. #64
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    Apr 2011
    Location
    Pakenham, Victoria
    Age
    53
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    350

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    Quote Originally Posted by Ch4iS View Post
    Thanks I used a spray gun only because it's cheaper to run, $50 for 4 litres from protec, the cans just don't seem to go very far, I find good quality cans like the rust guard from bunnings leave a better finish than with my spray gun, but they're about $14 a can. My HVLP spray gun is only a $20 internet special.
    Looks pretty good to me. Well done.

  6. #65
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    Oct 2013
    Location
    Europe
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    11

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    Very nice work ! congratulations

  7. #66
    Join Date
    Aug 2008
    Location
    Perth
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    31

    Default Midspan Stiffening

    [QUOTE=Ch4iS;1706227]Yea it's all 75x75x2.5mm. I'm thinking of using 50x50x5mm RHS for the support beam, possibly adding two, sufficient or beef it up? will need to still work out brackets ect. but it'll be butted up against the PFC so I can bolt angle pieces to it.

    Hi Chris,

    Refer below to my quick and approximate analysis.

    Image 1 is a 3D rendered view of the analysed model
    Image 2 is the static model with 3 loadcases - each point load is 100kg
    1. LC1 = front of the table at midspan,
    2. LC2=middle of the table and
    3. LC3= midspan of the side-channel

    The deflection results are given on the subsequent images:
    • Image 3 is Deflection of the table for LC1 - 0.38mm
    • Image 4 is deflection of the table for LC2 - 0.21mm
    • Image 5 is channel deflection for LC3 - 0.01mm

    Images 6 and 7 are deflections with midspan stiffener (50SHS2.5) for LC1 and LC2.

    The provision of 50SHS2.5 at midspan would balance and reduce the midspan deflections from 0.38 mm & 0.21mm to about 0.07mm (good).
    Doubling up the midspan support (2 x 50SHS2.5 side by side) or increasing to 75SHS2.5 is not effective as the O/A deflections are governed by the front and rear 75SHS2.5.
    100kg point load is quite high and the above deflections should conservative estimates.

    Hope that above helps.

    Regards
    Zvon



    CNC2.jpgCNC3.jpgCNC4.jpgCNC5.jpgCNC6.jpgCNC7.jpg

  8. #67
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    Feb 2008
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    Australia
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    988

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    Thanks for the help, zvon

    Those numbers look excellent, a table upgrade will definitely be on the list of improvements to do along with a full z axis/y carriage rebuild (some errors in machining I'd like to fix up)

  9. #68
    Join Date
    Jan 2012
    Location
    Australia
    Posts
    20

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    Hi
    nice build, can I ask what brand if extrusion you used for your gantry? I did a similar build a while ago and I used an 80x160mm extrusion but when I mounted the linear profile rails the rails were leaning into each other to much so it required a hell of a lot of shimming to get it right to lift the insides of the rails, have you had this problem? Cause I am thinking of changing out my profile to a different brand.
    thanks in advance
    chris

  10. #69
    Join Date
    May 2003
    Location
    Perth WA
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    3,784

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    Hi CNCChris, The 80 by 160 profile is expensive so I would be trying other options first. I wrap ally plate around my gantry beams as per the photo and that DCP_1432.JPGworks well.
    Cheers,
    Rod

  11. #70
    Join Date
    Jan 2012
    Location
    Australia
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    20

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    Hi
    thanks for the reply, I did put a 12mm aluminium plate on the front but when I bolted it down the plate pulled and warped to the same formation as the profile so that didn't work either.
    did you mill the front of the aluminium plate after it was bolted down?
    thanks
    chris

  12. #71
    Join Date
    May 2003
    Location
    Perth WA
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    Your extrusion must be bad to distort a 12mm plate. Note that the rails are attached to the plate and the plate is then attached to the extrusion and not the rails attached to the extrusion through the plate. My plates are not milled although that would be a very accurate way of doing it so long as it will never be disassembled and re-assembled down the track.
    Cheers,
    Rod

  13. #72
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    Feb 2008
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    Australia
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    Quote Originally Posted by CNCChris View Post
    Hi
    nice build, can I ask what brand if extrusion you used for your gantry? I did a similar build a while ago and I used an 80x160mm extrusion but when I mounted the linear profile rails the rails were leaning into each other to much so it required a hell of a lot of shimming to get it right to lift the insides of the rails, have you had this problem? Cause I am thinking of changing out my profile to a different brand.
    thanks in advance
    chris

    This piece is 80x120mm purchased from (linear bearings) Home back in 2009 (was a gantry from a machine which was never completed.) from memory it's $360 + GST per/M pricy stuff.

    I've only eyed it with a square at this point and didn't see any cause for concern, I will be looking to mount a plate on the front from 5083 cast plate like rod has done just to give the rails a better surface to mount on.

  14. #73
    Join Date
    Aug 2010
    Location
    Glenbrook NSW Australia
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    705

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    What I was looking at do when I build my new cnc was to lay the gantry level with the rail side up and where the rail are to fit, after all the hole are drill and tap then blocked up then flooding the front in two strip with epoxy and let it self level.
    Do the same on the y axis. This should be very flat surface for the rails I would think.....


    R
    vapourforge.com

  15. #74
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    May 2003
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    Perth WA
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    Hi Rusel, I have seen this attempted and it has ended up with having to flatten the epoxy afterwards. Daming up the perimeter is problematic as well as capillary action, voids and air bubbles and setting the item perfectly level. For me it is just introducing an error and I think the starting point is probably more accurate than a lot of work and expense. If necessary the rails can be shimmed away from the plate but the real question is what do you use as a datum to measure off. Unlikely any of us have access to a surface plate/table of the size required to ensure the rails end up perfectly flat and parallel.
    Cheers,
    Rod

  16. #75
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    Oct 2013
    Location
    melbourne
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    4

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    Quote Originally Posted by rodm View Post
    Hi Rusel, I have seen this attempted and it has ended up with having to flatten the epoxy afterwards. Daming up the perimeter is problematic as well as capillary action, voids and air bubbles and setting the item perfectly level. For me it is just introducing an error and I think the starting point is probably more accurate than a lot of work and expense. If necessary the rails can be shimmed away from the plate but the real question is what do you use as a datum to measure off. Unlikely any of us have access to a surface plate/table of the size required to ensure the rails end up perfectly flat and parallel.

    First post here

    If done right using resin can give very good results. May I ask what resin was used when you saw it?
    The resin to use is WEST SYSTEM resin with 209 hardener. This is a very low viscosity resin so it runs well. The 209 hardener is a super slow hardener so it gives the resin plenty of time to self level. As rodm pointed out making the channel so it doesn't drip is the trickiest bit. This is where I had trouble. However the end result was still far better, easier and faster then what myself shimming could achieve.

    You either have to have an extremely rigid frame or have the frame bolted down to the ground when you do the resin. Reason being if you bolt the frame down after it will flex, making the execise pointless. I bolted mine down first then did resin, means it will stay in that spot for now. If i want to move it I'll do the resin again.
    When working out how much resin to use aim for about 5-7mm thickness. Also try and get the frame as much level as possible before doing the resin.

    Here's where mine is at now. Can't wait to get back into next week when exams finish
    Attached Images Attached Images

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