Thread: Smiler's Build
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27-12-2009 #21
I would do a little more research on PVC v Ally or MDF...
Here's some data (MDF/PVC/Alu):
Tensile strength: 0.3/58/300 MPa
Youngs Modulus: 3.6/3/69 GPa
Density: .73/1.44/2.7 kg/m3
The MDF is half the weight and slightly more rigid against bending than PVC but will delaminate far quicker. MDF is also far cheaper than PVC (about 1/25).
Solid aluminium is 20 times more rigid than either MDF or PVC but weighs more (2 x PVC, 5 x MDF) but then it could be 1/5 the thickness of MDF but still 4 times more rigid.
So PVC's main advantage is in areas where the MDF is likely to delaminate under stress... eg where it has to be end-fixed or there is a strong perpendicular force retained purely by the MDF (not bolted through). Its not an obvious replacement in all areas.
The other main advantage of PVC compared to MDF is that it is available in a range of thicknesses up to 50mm.
I would potentially use PVC for:
- The table, where you want to machine the surface flat and avoid flaking.
- The gantry sides where I could use 40mm thick PVC and get twice the rigidity of MDF (then again I could use 2 pieces MDF bolted/glued together to get the same result at 1/2 the weight and 1/10 the cost)
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27-12-2009 #22
Additional info... looking at the data on the Direct Plastics site, if its rigidity you are looking for then Tufnol 1p13 is about 3 times more rigid than PVC or MDF but 25% more expensive than PVC (£155/m2 again £124/m2) but about the same weight (twice that of MDF). There may be other reasons not to use it tho...
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27-12-2009 #23
Jeff
Great looking machine and signs, I have two CNC4PC BOB's and both have been very easy to set up and operated flawlessly so far, as you know I am still in the early stages of getting my machine up and running so they have not been used in anger yet, also Arturo is very helpful and very quick to answer any questions.
Andy
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27-12-2009 #24
Supa! all round Jeff, really nice to see your machine go from start to finish and also the products its been making. Keep us updated with the pics when you make somthing new using the cnc machine its always nice to see, one question...
Why did you go with the supported rail for the Y Axis but guideway rail on the X ?
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27-12-2009 #25
I will certainly keep posting pics, I have a sign to do for a shop in Cumbria and that will be approx 2ft x 3ft sandwich board and it will have to be very special. It will also be the one I thnk I'll vdeo, I'm only sorr I didn't vdeo the"Tara" sign as it was a really nice job to work on.
I went with the guided rail for two reasons, first, the rails came up on the bay at the exact same time I decided to change from unsupported rail plus it was 25mm and new. The price (103 quid for two rails plus four trucks)was too good to miss. The second reason was I figured that the supported round rail is designed to take a load vertically and my Z axis weighs in at 60+ pounds with router and guided rail would be much more rigid. It also has the advantage of bringing the Z axis closer to the centre of rotation of the X axis taking a little load off the tool.
Answer 1, 3Nm wired in Parallel. I took the easy way out and bought the Driver Kit 1 from Zapp and I've been delighted with it.
Answer 2, Rack drive was the one recommended by the Solsylva plans and when you look at his plan book, the guy really has done his homework. He gives options for several types of drive, double ball / ACME screws, belt, chain and lists their pros and cons. The rack drive has the best accuracy/resolution/speed/cost envelope for my machine. A rack system is also easily extendable.
Answer 3, I can only report that the little bit of ally machining I did went very well in that it was very smooth and the finish was very nice. The guided rails have added so much rigidity. I didn't bother with measurements, it was just a manual cut and experimental. I'll do a proper job at the weekend and report back once I've designed and cut an ally webcam mount to replace the PVC one.
Answer 4, What would I do different.....
1 Do loads more research
2 Do loads more research
3 Do even more research.
4 ASK LOTS OF QUESTIONS OF PEOPLE WHO HAVE MADE THE MISTAKES
5 Know from day 1 what I wanted to make and how big the machine would need to be. I wasted loads of money buying bits and finding the machine had outgrown them before they got delivered.
6 No unsupported anything
As far as the machine stands now, I would not change anything. It far exceeds the hopes I had at the start.
Will do Dean, You'll like the router mounts. The slides on the 3612C plunge base are 20mm so all I used were two 20mm round rail mounting blocks and two 125mm long offcuts of 20mm round rail. Space them the same distance apart on your Z as they are on the plunge base, unscrew the fine adjuster on the router, pop the router off the plunge base and slip it onto the Z axis then tighten the locking lever, job done. I will also be adding a bracket to give a little more support to the router at the t
And to everyone else, thank you for the kind comments. This build is not over by a long way and then of course comes the plasma and the lathe and the......
Regards to all, Jeff.Nothing is foolproof......to a sufficiently talented fool!
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27-12-2009 #26
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27-12-2009 #27
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27-12-2009 #28
Got to remember where I live Lee
It is Gaelic script. When I gave it to my mate I said "that is actually a T not a C", he replied " I know, why would you think I thought it would be a C?" When these shapes are a part of your culture, you don't need to be told what they are
Regards, Jeff.Nothing is foolproof......to a sufficiently talented fool!
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27-12-2009 #29
Hey Smiler,
I just put in my order for one of DIY Cnc's BOBs, and I'm a little concerned that you're going with a different make. Was it a user error, or did it give up the ghost on its own? :D. Should I be thinking about canceling my order, and going with someone else?
I really like what you've done...
Dave.
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27-12-2009 #30
User error Dave. My main BOB is a DIYCNC Uniport and I'm very pleased with it indeed. Buffered outputs for 4 drivers and three relays onboard that don't need external power. The original one was an Optoport which I shorted out trying to wire in a relay in my hamfisted way. Roy repaired it FOC and I put it back in as Port2 so I could have some extra inputs to Mach. Well, I managed to do the same trick and shorted out the board AGAIN and I just can't face asking Roy to fix it again. It was my own stupid fault "tinkering" when I should have just said "right, that's the controller finished". What I was thinking of doing was just getting an opto-isolated BOB which can use pins 2-9 as inputs as that would be what I really wanted and DIYCNC don't do them or I would be buying one from Roy ASAP.
If you've seen my other post this morning about the U-HID interface, well that would mean I don't actually need another BOB at all and that might be the way I go now.
Don't think you will go wrong with DIYCNC, they are very well made boards.
Regards, Jeff.Nothing is foolproof......to a sufficiently talented fool!
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