. .
Page 1 of 4 123 ... LastLast

Hybrid View

Previous Post Previous Post   Next Post Next Post
  1. #1
    Hello again everyone,

    My first CNC design was, in hindsight, perhaps a little bit ambitious for a first build. After building one of the sides I realized that welding was the only realistic option and that my current workshop just wasn't big enough to fit the machine (and it would weigh too much for the floor).

    Rather than wait for the workshop to be built I thought I'd come up with a new design for a more modest sized CNC machine that will fit in the space I currently have. There's not much to see yet but I was hoping to get a bit of feedback on the pulley arrangement for the x-axis as this is an area that I'm not very familiar with. Firstly some pictures...

    Click image for larger version. 

Name:	2013-08-15 overview.png 
Views:	1268 
Size:	291.7 KB 
ID:	9461
    Click image for larger version. 

Name:	2013-08-15 bottom.png 
Views:	918 
Size:	156.0 KB 
ID:	9460
    Click image for larger version. 

Name:	2013-08-15 back closeup perspective.png 
Views:	762 
Size:	97.9 KB 
ID:	9457
    Click image for larger version. 

Name:	2013-08-15 back closeup.png 
Views:	690 
Size:	19.6 KB 
ID:	9458
    Click image for larger version. 

Name:	2013-08-15 back.png 
Views:	644 
Size:	54.4 KB 
ID:	9459

    The frame is going to be all extruded aluminium if possible. The blue sheet forming the bed is 600x600mm to (hopefully) give a cutting area of 400x400mm. Z axis travel will be fairly limited, perhaps as little as 50mm, as this machine is being designed to mainly cut aluminium.

    The x-axis rails are SBR16 although I could probably fit SBR20 if necessary. The rails are sitting on 60x90 heavy extrusion as sold by KJN. There's 180mm between bearing block centres.

    The ball screws are currently spec'ed as 1605 with 16 tooth HTD5 pulleys on the end (with extra long end machining). The stepper will be a nema23 but I've not picked one out yet. The stepper is fitted with a 32 tooth HTD5 pulley to give a 2:1 ratio.

    The stepper and the two idler pulleys are mounted on a 10mm aluminium plate. For build simplicity the idlers are used to take up the slack on the belt rather than the stepper. The stepper is mounted using stand off legs. The belt length (at central idler adjustment) calculates as 1736mm

    The plan is to have this machine standing vertically, or perhaps wall mounted, so that the x-axis belt is at the top.

    My questions so far...

    1. Does the belt make enough contact with stepper motor pulley? I'd guess about 12 to 15 teeth are in contact with the belt.
    2. How is the 32 tooth pulley attached to the stepper shaft? There's only 15mm of shaft on the stepper so I'm guessing it will have to be a taper lock (also Belting Online don't bore 32 tooth pulleys at 6.35mm).
    3. Where can I get idler wheels from? Neither Belting Online nor Bearing Station seem to do them. I'm tempted to follow Jazz and use bearings and penny washers...


    Cheers :-D

  2. #2
    Quote Originally Posted by Wobblycogs View Post
    I'm tempted to follow Jazz and use bearings and penny washers
    Nothing wrong with Bearing and penny washers they've been working fine for 6yrs now.!! . . . . That bit of string for a belt won't work thou. .

    Ok so first don't go with 1605 and 2:1 ratio it's not need and you'll want more speed than that.
    Direct 1:1 will be enough for cutting aluminium. If you want to go 1:2 then buy 1610 then you'll get same resolution and 1:1 speed has 1605 but double the torque of motors so lots of torque while cutting at low speeds. You'll rarely cut above 1500mm/min in aluminium.
    With 1:2 ratio on 1610 then it's a simple switch of pulley if you want speed for routing, plastics etc.

    Next the frame is no where near strong enough for cutting aluminium. Beef up the lower portion, I'd suggest an outer frame with inner cross braces. Really those corner angle brackets are rubbish so I'd think about some good strong plates with plenty of bolts.

    If your going vertical then you'll need to think about the gantry, Z axis has depending on which way you orientate it will depend on how chips collect on surfaces etc. You'll certainly be wanting to put covers on Z axis and belts to help stop chips collecting if your putting belts at top.
    It's like this Aluminium chips fly every where and they go up before coming down so just think about what they will land on and or were could collect.
    In general it's not a problem more of an annoyance because on my machine the Z axis front plate faces down and if doing again I'd face up and put cover on because the chips collect on rear of front plate. Basicly Z axis is on wrong side of gantry facing down, I'd put on top side facing up.

    Hope this helps.
    Last edited by JAZZCNC; 15-08-2013 at 08:39 PM.

  3. #3
    Thanks, as always Jazz your reasoning makes perfect sense on the ballscrews so I'll change then to 1610's. Hopefully this new design will be stiff enough. As for the bely I was thinking I could save a bit of money if I just used a bit of string pulled tight ;-)

    Everywhere you see a hole that looks like it should have a bolt there will be one.

    This shot is of the base with the new base plate removed showing the new end pieces on the bed rails - these will be bolted on. The corner brackets are still there but they are more to affix the x-axis to the bed rather than hold the whole thing rigid.
    Click image for larger version. 

Name:	2013-08-15 strong insides.png 
Views:	587 
Size:	218.5 KB 
ID:	9472

    The back plate has grown "ears" and bolt holes. Long bolts will run down into the x-axis and the rails at the end of the bed.
    Click image for larger version. 

Name:	2013-08-15 strong back.png 
Views:	549 
Size:	139.8 KB 
ID:	9469

    There's a new front plate (10mm) which again has bolt holes for the x-axis and the bed.
    Click image for larger version. 

Name:	2013-08-15 strong front.png 
Views:	550 
Size:	239.3 KB 
ID:	9471

    Finally the base has been covered in a 5mm sheet of aluminium and bolted all over the place for bracing.
    Click image for larger version. 

Name:	2013-08-15 strong bottom.png 
Views:	554 
Size:	106.8 KB 
ID:	9470

    I forgot to mention in my first post but the blue bed piece will also be bolted to the bed for bracing.

    The only downside I can see of this is chips will accumulate on the front plate, a small price to pay if it's cutting aluminium accurately!
    Last edited by Wobblycogs; 15-08-2013 at 06:29 PM.

  4. #4
    Jazz,

    sorry if I'm getting this completely wrong, but the op wrote a gearing ratio of 2:1, but also has written and drawn a 32 tooth pulley on the motor and 16 tooth pulley on the screw. Doesn't this setup actually give him a 1:2 ratio, so 1 turn motor gives him 2 turns screw. So theres plenty of speed, which isn't needed as you say 1:1 is ample for aluminium, the op's main working material.

    Adil

  5. #5
    I think I've got the ratio the wrong way around, it should probably read 1:2. To clarify there is a 32 tooth pulley on the stepper and 16 tooth pulleys on the ballscrews.

  6. #6
    Quote Originally Posted by Iwant1 View Post
    Jazz,

    sorry if I'm getting this completely wrong, but the op wrote a gearing ratio of 2:1, but also has written and drawn a 32 tooth pulley on the motor and 16 tooth pulley on the screw. Doesn't this setup actually give him a 1:2 ratio, so 1 turn motor gives him 2 turns screw. So theres plenty of speed, which isn't needed as you say 1:1 is ample for aluminium, the op's main working material.
    Yes but I knew what he meant because of the pulley sizes but I copy and pasted so didn't correct it sorry.!!

    Edit: Corrected now..!
    Last edited by JAZZCNC; 15-08-2013 at 08:39 PM.

  7. #7
    The design has progressed a bit so I thought it was time to get a bit of feedback...

    Click image for larger version. 

Name:	2013-08-17 perspective.png 
Views:	690 
Size:	192.5 KB 
ID:	9523 Click image for larger version. 

Name:	2013-08-17 bearing block placement.png 
Views:	702 
Size:	96.3 KB 
ID:	9524 Click image for larger version. 

Name:	2013-08-17 top.png 
Views:	634 
Size:	111.1 KB 
ID:	9525 Click image for larger version. 

Name:	2013-08-17 back.png 
Views:	608 
Size:	63.8 KB 
ID:	9526 Click image for larger version. 

Name:	2013-08-17 side.png 
Views:	675 
Size:	90.3 KB 
ID:	9527 Click image for larger version. 

Name:	2013-08-17 front with dimensions.png 
Views:	569 
Size:	51.4 KB 
ID:	9529

    I've decided to try to increase the maximum material thickness to more like 100mm (up from 50mm before). To achieve this though I seem to have ended up with an unusual bearing block placement on the z-axis, see image 2. The idea is to be able to lift the z-axis high enough so that the bottom of the gantry is the limiting factor for the material depth. As drawn I have 180mm top to bottom between the z-axis bearing blocks but I could easily increase this - I was thinking 250mm would compensate for the additional over hang of the z-axis.

    The gantry has changed design several times . It started out as two pieces of 45x45 heavy (a bit like this) then got changed to two pieces of 60x90 heavy , then to a single piece of 90x90 heavy.

    I finally settled on two pieces of 45x60 heavy with a backing plate of 10mm aluminium, the unsupported span is 610mm. The deflection calculator on the Metallin website (using the closest match) seems to think the z-axis deflection should be ok. Using 60x90 heavy would reduce deflection, I'm sure, but it was expensive and reduced the x-axis cutting. I think this is probably a fair compromise.

    The belt arrangement of the x-axis has been improved. The ratio is now 1:1 and there's better belt contact with the stepper pulley.

    I've not added the y or z-axis steppers into the diagram yet (should be fun). Also still to be drawn is a chip guard for the y-axis screw. There will be a thin plate with a long slot (and maybe brushes) for the y-axis connection to the z-axis assembly.

  8. #8
    I'm all ears.......
    Neil...

    Build log...here

  9. #9
    I ordered my ballscrews off Chai last week, I also bought a set of collets off him but got 2.5m of energy chain off fleabay...going to be like Christmas soon with all this equipment arriving. Best order some steel Monday and get welding...
    Neil...

    Build log...here

  10. #10
    After my bracket making endeavours the other week I've been thinking that it's probably better if I just get the majority of the pieces cut professionally. I think I probably could just about cut the pieces myself and end up with a working machine but I'd be old and grey by the time I finished (or I'd end up buying a milling machine).

    A benefit of getting the parts made is I don't have to worry about cuts that would be difficult for me to make. With that in mind I've changed the design slightly. The parts in eye watering green have been upgraded from 10 to 15mm. The brace for the gantry is gone in favour of a single stronger side plate (there will be M5 bolts through the side plate into the front and back gantry plates and the base plate).

    Click image for larger version. 

Name:	2013-11-16 perspective 2.png 
Views:	303 
Size:	94.4 KB 
ID:	10774Click image for larger version. 

Name:	2013-11-16 perspective 1.png 
Views:	339 
Size:	145.0 KB 
ID:	10775

    I was thinking about maybe getting the parts water jet cut by a local company that could also supply the aluminium for the job. Unfortunately I have no idea how much water jet cutting costs, I'm guessing it's not cheap though. The other option would be to find some kind soul around these parts that would cut them for me.

Page 1 of 4 123 ... LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. BUILD LOG: Wobblycogs CNC Mk1
    By Wobblycogs in forum DIY Router Build Logs
    Replies: 91
    Last Post: 02-01-2013, 07:38 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •