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Thread: A New CNC Build
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24th December 2008, 09:23 AM #46Senior Member
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Speaking of Sketchup, how does it go for simple 2D stuff ?
Machine is looking great Geoff !
Cheers.
Russell.
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24th December 2008 09:23 AM # ADSGoogle Adsense Advertisement
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24th December 2008, 10:00 AM #47SENIOR MEMBER
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You can do 2d but its still in 3d you just dont add a dimension. Im sure there is a 2d perspective but I have never needed to use 2d alone.
You can give it a go its free to trial and use, just if you want to export to DXF ect. you need to buy the pro version, I dont think there are any other limitations.
http://sketchup.google.com/
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20th March 2009, 12:25 AM #48Simsy
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Hi All
It's been a long long time since I've posted on the forum or done any work on my machine. Over the last nearly three months, I've had some fairly significant other issues to contend with that precluded any progress on it.
However, I'm happy to say that I've pretty much got past those issues and am now ready and fit enough to get back into it.
One positive (well that's the way I want to look at it) is that I have been forced to make the decision to semi retire which means that I now only work two days a week. I'm going to have lots of extra leisure time to hang out in the shed. Of course there is a downside, and that is the reduced income available to me. Still, we can get by.
Anyway, one more week to go and it's back to the build, and a lot of catchup on the forum. Next week though, I'm off to Melbourne with my son for the F1 Grand Prix.
After that, it's out to the shed, uncover the machine and get rid of the dust and cobwebs. Then, lots of pictures and posts, AND no doubt many appeals for advice as I try to get this thing cranking.
So, glad to be back.
Cheers to all.
Geoff
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20th March 2009, 12:31 AM #49GOLD MEMBER
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Hi Geoff,
Glad to hear you are on top of things now.
Looking forward to seeing your machine progress.Cheers,
Rod
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20th March 2009, 09:18 PM #50
Hi Geoff,
Good to see, there is something to be said about early retirement too.
I'll keep a check on you now
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3rd April 2009, 12:19 PM #51Simsy
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Thanks guys. OK back into it.
In my last post back in December, I'd just finished the gantry, but hadn't yet mounted in on the X axis rails. Now I've mounted it on the rails and I'm not happy with it.
The gantry moves very freely and smoothly which I'm very happy about, but I'm very surprised at the amount of flex in it from one side of the machine to the other. If I clamp one side of the gantry solid, I can quite easily move the other side by up to as much as 7 or 8mm. Bearing in mind that I was going to have only one central ballscrew on the X axis, that's a lot of flex at either end of the gantry.
So, I've got two alternatives. Either use two ballscrews, one on either side of the machine, or beef up the gantry. I'm leaning towards the latter, but if any one has other ideas, please let me know.
The gantry, as mentioned previously is just an I beam of sorts, consisting of a 160x10 web and 50x10 bar bolted along the top and bottom. I'm thinking of replacing the 50x10 with 80x10 or 100x10 to stiffen things up a bit. Also, the gantry sides (160x10) have a lot of flex in them, allowing them to twist slightly. I thought I might beef them up by bolting a 100x10 bar on the outside.
Don't know if that makes sense. I'll try to put up some pics later on to explain.
Any suggestions appreciated.
Cheers
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3rd April 2009, 02:01 PM #52GOLD MEMBER
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Hi Geoff,
Yes I agree the best solution is to beef up the gantry rather than a second ballscrew and motor. Dual axes create a complexity and cost you do not need on a machine your size.
Ok the problem is the joint between the gantry sides and the Y axis beam. You have used 50mm wide strips so therefore you probably only have 40mm between the two cap screw. A wider plate will solve it for you but I hate to see all that good work undone particulary since you have mounted the rails on those strips.
You mention nothing about an underbelly plate joining the gantry sides - the plate that will join the X axis ballscrew to the gantry. This is where I have found that a full width plate the same width as the gantry sides removes all the racking. It only needs to be say 5mm plate or whatever you can get your hands on. If you let me know the size I have a bit you can have. Make sure it is fixed with at least three cap screws both sides - four is better.
If this does not fix it all then perhaps a gusset at the top where the gantry sides join the Y axis beam - not sure how that can be done though so just throwing this in to get your grey matter working. You still have to fit a cable tray so maybe with a bit of thought this could be a beefed up cable tray and used to stiffen the top of the gantry.
For the moment I would leave the gantry sides as they are as I have a feeling that will be resolved by taking the racking out.Cheers,
Rod
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3rd April 2009, 03:00 PM #53
I think Rod is right here
Definitely needs a gantry plate so both sides are together for a ballscrew in the middle... Should fix any racking then...
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4th April 2009, 12:23 AM #54Simsy
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Thanks Rod and Bob.
Sorry, forgot to mention the underbelly drive plate. The flex or racking I mentioned was with a 6mm drive plate fixed on the bottom of the gantry, the same width as the gantry sides and fixed with three cap screws at each end.
Rod, I don't really have a problem with replacing the top web of the I beam with something a bit wider. A bit of work, but worthwhile, I think. Someone once told me that sometimes when something doesn't work out, it's better just to start again rather than try to fix it and end up with a lesser result. I think it was a very good piece of advice.
I've also given some thought to a cable tray and have considered another 50mm web on the back of the I beam so it's more like an E beam with the Y axis ballscrew running in the bottom half of the E and the cable tray in the top half. It going to take a bit of figuring out though.
Wish I could use a CAD package. Had a bit of a play with Sketchup some time ago, but other things took precedence. I'll have to get back to the tutorials and give it another try. It would be great to be able to illustrate the different design alternatives for my machine.
Anyway, thanks for your suggestions. I'll have another look over the weekend.
Cheers
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4th April 2009, 02:22 AM #55GOLD MEMBER
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Hi Geoff,
That is 10mm thick material and only a short span for the combined section you have fabricated so it is unlikely the beam itself is flexing. I think the problem is in the joint between the beam and the gantry sides.
Just to humor me put a couple of washers under your cap screws at the connecting points. It is possible that you have bottomed out in the tapped hole and you are not getting full clamping force of the cap screw. Check the bottom plate for the same thing. Another thing you can try is running a bit of say 40 by 40 x 6 angle at the intersetion of the vertical gantry plate and the gantry sides.
As you say a wider plate on the Y axis would fix it because you will be creating a wider fixing between the two components but I did take in to account the need to wrap a box around this wider section for the Z axis as being not as desirable as the design you have.
To satisfy your curiosity flex the two sides of the gantry and clamp it in place - ie with the twist in it. Put a straight edge along the Y axis and see if it is bowed or straight. That should tell you what is happening.
Let us know how you get on. At least the weather is good for tinkering in the shed.Cheers,
Rod
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7th April 2009, 01:18 AM #56Simsy
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Thanks for the suggestions Rod.
Tried washers under the bolts. Didn't help as none of them were bottoming. The straight edge proved the X axis to be straight along the top and bottom flanges of the I beam, but when clamped with a twist in the gantry, they're not parallel which means the vertical web of the gantry is actually twisting.
I'm pretty sure I can eliminate the twist, but I don't think I can explain what I've got in mind.
I'll give it a try and report on the results.
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7th April 2009, 01:41 AM #57GOLD MEMBER
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Hi Geoff,
Good to see you have tracked the problem. Much easier to fix if you know what you are working against. I think I know what you are saying but not 100% sure so will wait until you report back.
Hope the solution is easy.Cheers,
Rod
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13th April 2009, 12:29 AM #58Simsy
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Spent a bit of time playing around with the gantry, but ended up deciding to give it a rebuild as there were some issues with the accuracy of my construction, and also some deficiencies in the design.
I came to the conclusion that a rebuild would be more effective than trying to rectify something which, in the end, I wouldn't be happy with.
I've spent quite a bit of time in the shed in the past couple of days, and, in between jobs for SWMBO, I've managed to get a fair bit done, but it takes a lot of time when you're not well equipped for working in metal and have to do everything by hand. This time though, I've gone to great pains to ensure better accuracy.
By next weekend, I should have a new gantry on the machine, and I'm confident racking and flex won't be an issue.
With any luck, I might even get the Z axis mounted. (Already built).
Now, a question. Some months ago, I tried cutting some aluminium on my bandsaw and ended up destroying the blade. I didn't use the slow speed, and I'm assuming that was the problem, along with not using a lubricant. I need to try it again, but what kind of lubricant should I use that's not going to contaminate the tyres on my bandsaws wheels? I don't want to use a silicon based lubricant which could find its way onto any timber I run through the saw. What do I need to look out for?
I'll post some pics of my new gantry when I finish getting it together.
Cheers
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13th April 2009, 12:53 AM #59GOLD MEMBER
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Hi Geoff
I agree with your logic- if you have a nagging thought that it is not the best then rebuild now. Much easier than doing it later when you have to strip and alter the electrics and other add ons. I am glad you posted this as it has made up my mind to strip down my first machine and rebuild the gantry. I was going to just replace the rails on Y but I would be selling my son (new owner) short if I did that.
On a bandsaw I don't use lublicant as the blade is slow enough not to cause re-melt. You could try WD40 or CRC or even kero but as you say you would need to clean your tyres afterwards.
I would guess you had the blade running too fast with your previous experience but don't rule out a blunt or low quality blade. Heat would have been the cause of the problem as ally cuts much like hardwoood on a bandsaw and doesn't seem to wear the blade any worse.Cheers,
Rod
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13th April 2009, 12:58 AM #60Simsy
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Thanks Rod
I just thought it better to rebuild than to chase a solution I may not find.
Thanks for the bandsaw advice. I'll give it another shot on slow speed and see how it goes. If I can get away with it, I'd much rather go without using a lubricant. I've got spare blades now, just in case.
Cheers
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