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  1. #11
    "Winging it" and "on the cheap". It's like your writing my obituary! 🤣

    I like to make things out of what I can find which I have found does sometimes lead to doing things twice or 'learning from your mistakes'

    The shorter drive belt on the robot is stationary, going around the moving driven pulley so I think that would be worth trying.

    The long belt was on the full 6m of ali. I'm struggling to remember if that was stationary or moving. I think probably moving as the motor was on the end of the rail not the moving carriage. I think if I alter it to be stationary I could put one either side. If your doing this can you put a motor each side and run them as a pair or is it better to physically link them with a shaft?

    Your eight, I need to do some planning, I will look at the links and play on cad

  2. #12
    Quote Originally Posted by John McNamara View Post
    G'Day Kitwin

    Happy New Year

    The Men's shed machine was built on a Budget, The rails and belts remain untouched to this day.
    The only changes made are the spindle updates, and recently it is mounted on a new stand.

    The machine was designed for woodworking and plastics, and light metals. 99% of the work is wood. Fully supported round rails are fine for this sort of application. The forces created by wood routing are fairly light. If I were designing a metal focused machine I would consider profile, Hiwin type, rails and ball screws.

    The local Council has supported the men's shed with work, making chunky road signs out of timber sleepers. The machine was used to cut the deep lettering moving the wood along in stages as the signs are very long.

    It was also used to cut deep pockets in about 2 metres long 100x100mm recycled plastic posts, there were hundreds of them! This was to make a kind of post and rail fence.

    Then there is all the members projects.

    If you study the video the long axis timing belt's (Steel stiffened) and Joined to be in tandem by a cross shaft (Note the torsion tube). are fully supported on the bed to avoid vibrating if suspended, rising up only at the drive point on the carriage. The belts are stationary. note the tensioner arrangements. These belts were were properly tensioned at build time, so far they have not required re tensioning.
    The Z axis uses a 16mm ball screw.

    It should be noted that all rotating parts were supported by Flange or snap ring type ball bearings clamped by laser cut retainers into the laser cut frame. Study the images. This was a big contributor to the overall accuracy. Also note the timing pulleys were carefully bored.

    All in all a low cost design that works. It met and excelled the design criteria.

    Regards
    John
    Nice to hear from you John, a very happy new year to you and yours.

    It's good to have feedback about the performance of such a budget machine over several years of use, it has obviously proved well worth the investment of both time and money. Maybe not fast enough for time-critical commercial use but that's not what most newcomers to this forum are looking for. You have clearly managed the balance between cost and performance by producing an excellent design. My signature used to be a quote from the duke of Wellington: "An engineer can do for ten shillings what any fool can do for a pound".

    Re the belts: I think this has come up before on the forum but one option to help avoid stretching of long belts is to glue a piece of pre-tentioned belt onto the frame so that the teeth of it and the driven belt are engaged. This locks most of the belt in place and only the length rising to the pulley can stretch. There is a name fro this idea, but I can't recall it at present.

    I asked about wear on the linear bearings as I had to replace a couple of bearings on my machine after not that much use, though I suspect this may have been due to excessive strain from poor alignment.

    Regards
    Kit
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  3. #13
    Hi Kit

    I guess you are referring to the Everman Belt system.
    An interesting design Idea, Patented.

    Keeping the join between the belts clean is important. Wood chips will have to be kept out.

    It is also worth noting that timing belts do not like bending backwards over a tight radius. The reason I used a pair of largish ball bearings. I cant remember the exact size! Maybe 60mm. We used steel cored European belting Breco? Not no name Asian, You can look up the minimum bending specs on their website.

    https://www.google.com/search?q=Ever...h=720&dpr=1.25

    Regards
    John

  4. #14
    Quote Originally Posted by John McNamara View Post
    Hi Kit

    I guess you are referring to the Everman Belt system.
    An interesting design Idea, Patented.

    Keeping the join between the belts clean is important. Wood chips will have to be kept out.

    It is also worth noting that timing belts do not like bending backwards over a tight radius. The reason I used a pair of largish ball bearings. I cant remember the exact size! Maybe 60mm. We used steel cored European belting Breco? Not no name Asian, You can look up the minimum bending specs on their website.

    https://www.google.com/search?q=Ever...h=720&dpr=1.25

    Regards
    John
    Everman, that's the one.

    Like every other option you can try, whether belts work well or not will depend on the details of the design and the precision of your requirements.
    An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.

  5. #15
    Hmmm this post got me thinkin!

    Re Belt Drives....

    This design, link below, will allow the drive to be preloaded using 1 full length fixed open ended belt and a conventional belt with teeth facing out.

    If you study the design you will see that the two sections in contact with the fixed belt can be moved towards or apart from each other thus changing the effective pitch of the small belt sections. This will enable a small amount of preload to be set.

    Easy enough to do with a few ball bearings.

    https://www.youtube.com/watch?v=NJZ7YVHRwAM

    Regards
    John
    Last edited by John McNamara; 03-01-2022 at 04:40 AM.

  6. #16
    Out of interest do people consider a 2.2kw spindle enough?

    I already have a spare inverter that will run that and an er20 collet set so there would be a cost saving there.

    If its not up to it I will plan for a 4kw now and buy a new inverter. I dont want to waste money on the 2.2kw spindle if its going to be limiting.

  7. #17
    Quote Originally Posted by Cynic-al View Post
    Out of interest do people consider a 2.2kw spindle enough?

    I already have a spare inverter that will run that and an er20 collet set so there would be a cost saving there.

    If its not up to it I will plan for a 4kw now and buy a new inverter. I dont want to waste money on the 2.2kw spindle if its going to be limiting.
    It Depends on the size of cutters you want to use and how aggressive you want to cut.? they can be pushed more than people realize and are very reliable considering the low cost.
    Also, remember everything needs to scale accordingly so if you're using a larger spindle it will be heavy and your z-axis, motors, and gantry, etc will need to match.

    John said it before and he's perfectly correct the machine is only as good as the sum of its parts or its leakest link so the Z-axis and spindle are IMO THE most important area, get this wrong, and doesn't matter how good the rest of the machine the quality of parts that come off it will always be shit.!
    -use common sense, if you lack it, there is no software to help that.

    Email: [email protected]

    Web site: www.jazzcnc.co.uk

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