CNC Having a go

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Postby gary » Sun Feb 10, 2013 3:38 pm

Hi Harry, yes I use the double sided tape quite a bit - it works very well.

Harry I was just looking over your pictures again and I noticed it seems you are using "galvanised" all thread.

I am not saying it won't work but the galvanised thread offers a great deal more resistance to the nut than does the zinc all-thread. In addition I have found that a lot of the galvanised all-thread has great lumps of "galv" in places which will need to be cleaned off.

Running a "thread chaser" or die over it may help although that will likely remove quite a bit of the galv and hence may cause the threaded rod to rust.

Also it looks as though it is a 5/16 or 3/8 rod. Nothing wrong with that but be aware that as a result of that it will have a coarser thread and using a coarser thread will give you less resolution than the finer 1/4" all-thread - 20 tpi that I use.

Unfortunately the zinc plated all-thread is only available in Australia in imperial sizes - I personally don't find that a problem - but a younger chap like yourself may object to it. ;-)
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Postby Harry Dalek » Sun Feb 10, 2013 5:04 pm

gary wrote:Hi Harry, yes I use the double sided tape quite a bit - it works very well.


Thats good really meaning the high speed cutting doesn't move it out of place , i would said before it would need clamping down for sure but looks like not for that stuff .

Harry I was just looking over your pictures again and I noticed it seems you are using "galvanised" all thread.


Yes i am for 2 reasons i wanted Brass but could not afford it and every thing else they sold was bent !!!!!!!!!!!!!!!!!!!!!!!!!!

I am not saying it won't work but the galvanised thread offers a great deal more resistance to the nut than does the zinc all-thread. In addition I have found that a lot of the galvanised all-thread has great lumps of "galv" in places which will need to be cleaned off.


I have given it a run its not to bad Gary thats even before even oiling of greasing it seems to work well on both hand turning and connecting my drill...but yes its not the type of thread i wanted .


Running a "thread chaser" or die over it may help although that will likely remove quite a bit of the galv and hence may cause the threaded rod to rust.


I hope it works i was going to grease it up for good movement ...one thing to which is a problem you shouldn't really use different metals together as they eat each other away i think its faster than normal rusting.


Also it looks as though it is a 5/16 or 3/8 rod.


It fits just right in the bearings Pot luck for me more that choosing right.
I was thinking if i got it to small and fine it might be to slow also looking at sizes other people were using also.

Nothing wrong with that but be aware that as a result of that it will have a coarser thread and using a coarser thread will give you less resolution than the finer 1/4" all-thread - 20 tpi that I use.


Perhaps it was a question i should of asked mmmmm i will have another think about this before moving on .
Does steeper motor speed and type and micro stepping in the program for the motors a factor that might make up for it ?

Unfortunately the zinc plated all-thread is only available in Australia in imperial sizes - I personally don't find that a problem - but a younger chap like yourself may object to it. ;-)


Well just a little least i know where to get the nuts for them ! 1966 was a bad year for me :?


I tried the nuts on the thread to see if they move together works well perhaps i just need a welded bracket between 2 or 3 spaced....there seems little play in the nut on the thread a very good fit with also good movement .

I was planning on a bracket for the nuts on the thread sort of T bracket where the length of the T is welded on the nuts and the top of the T is long and bracket is bolted to both sides of the bearing movement brackets ...that way i can have a board base not moving and the Dreamal is on the x and y axis moving along .


Now this is a Question i am not sure about what is best , i noticed mainly on the small designs the Y axis is bolted to the frame and the x axis bottom base moves .
The larger ones the base doesn't move as the Y is on the x bearing mount
is it much the muchness or is one better than the other for cutting ?
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Postby gary » Sun Feb 10, 2013 5:18 pm

Yes a microstepping controller may indeed more than make up for it. I shouldn't worry about it too much - just thought I'd let you know just in case.

I am not sure if there is any real difference between a moving bed and a moving gantry - it seems the smaller machines tend to be moving bed and the larger ones moving gantry.

I suppose at the larger size it is better to be moving a router (more or less a fixed mass) than a potentially large item to be milled.
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Postby Harry Dalek » Tue Feb 12, 2013 7:39 pm

gary wrote:Yes a microstepping controller may indeed more than make up for it. I shouldn't worry about it too much - just thought I'd let you know just in case.

I am not sure if there is any real difference between a moving bed and a moving gantry - it seems the smaller machines tend to be moving bed and the larger ones moving gantry.

I suppose at the larger size it is better to be moving a router (more or less a fixed mass) than a potentially large item to be milled.


Yes this had me wondering Gary both have their good and bad points just wanted to make sure before moving on .

The T Bracket idea is a bit like this idea in the picture so i will work on that bracket next, i can see one nut on the thread works but it would be more stable as you said with a long nut or in my case a few spread and welded under that T bracket .

I have more bearings now to finish the Y and Z when i get around to it .
Attachments
hr_y_axis.jpg
hr_y_axis.jpg (171.01 KiB) Viewed 2535 times
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Postby Harry Dalek » Sat Feb 16, 2013 8:54 pm

Well i ended up skipping the thread work as i had to work out the Y axis movement making that changed my X axis.

I have flipped the angle steel pointing downwards this saves me making the top of the T bracket .

I have worked out the Y axis rail part just need to weld that and have started making the bearing movement for it .


The Bed will be between the X and Y a little gap i am not sure if i will increase this just a matter of a longer bracket but this will do for now think most of the stuff i will work with will be pretty flat anyway .
Attachments
P1040732.JPG
My Y axis rails the angle steel the v point is on the horizontal each side of the a square post this let me angle them correctly
P1040732.JPG (172.12 KiB) Viewed 2525 times
P1040731.JPG
front view
P1040731.JPG (176.41 KiB) Viewed 2525 times
P1040734.JPG
How the bearings will go have to weld a bracket on ,its a copy of the x axis ones
P1040734.JPG (130.41 KiB) Viewed 2525 times
P1040735.JPG
A better view of the idea so far
P1040735.JPG (135.67 KiB) Viewed 2525 times
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Postby Harry Dalek » Sun Feb 17, 2013 3:18 pm

Today i finished off the Y axis I have used a bit of steel in this project with the bearings every thing still moves with little effort which is good.
Heres some pictures a video for those interested .
Tell you this WD 40 stuff sure is strong takes the paint right off my angle steel WHOOPS.
Attachments
P1040736.JPG
P1040736.JPG (185.78 KiB) Viewed 2516 times
P1040737.JPG
P1040737.JPG (163.97 KiB) Viewed 2516 times
P1040738.JPG
P1040738.JPG (168.51 KiB) Viewed 2516 times
P1040740.JPG
P1040740.JPG (132.45 KiB) Viewed 2516 times
Untitled.avi
video of the movements
(3.18 MiB) Downloaded 95 times
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby gary » Sun Feb 17, 2013 3:55 pm

Looking solid Harry, might be an idea to strip that paint off once and for all - you don't want it "gumming" up the works.
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Postby Harry Dalek » Sun Feb 17, 2013 4:19 pm

gary wrote:Looking solid Harry, might be an idea to strip that paint off once and for all - you don't want it "gumming" up the works.


I wish i had a grit blaster one of my old jobs was doing that at BHP could of done it for free if i had done this 30 years ago .

Yes i will get it off the rails for sure .

One axis to go and some threading to think about :roll:
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Postby gary » Sun Feb 17, 2013 5:32 pm

Do you have an issue with your drive screw mechanism? It's relatively straight forward. The two main issues are the couplers (to connect the drive screw to the stepper), and the anti-backlash nut. The latter we have already discussed, the former I solved by biting the bullet and buying some Lovejoy jaw couplers. You can use rubber tubing to do the coupling but eventually you will want to go to the better type of coupling. If you decide on Lovejoy couplers (or similar) you will almost certainly find you will have to import them from the US- they ARE available in Australia but when I researched them they were about 5-6 times the price of the same item in the US. Alas,, shipping prevents them being very cheap ($10 each in the US) but it's still better than to give money to the robbing bastards here.

Do NOT be tempted to buy those couplings from Jaycar - they are way overpriced and not suitable for this application.

NOTE! It is essential that the coupling prevents any significant sideways (lateral) forces from reaching the stepper otherwise the steppers will not last long. All of the lateral force should be absorbed by the bearings either end of the drive screw - ideally these would be thrust bearings but skate bearings seem to do well and are very cheap and readily obtainable.
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Postby Harry Dalek » Sun Feb 17, 2013 8:32 pm

gary wrote:Do you have an issue with your drive screw mechanism?


I Know i can do that part but since i have no real plans for this thing making it as i go with parts i have handy and what works and such i have to do that part after i do the Axis movements ,then i can wack those threads in.

I have been thinking about should i rethink the thread size should i try and make it wood free .

It's relatively straight forward. The two main issues are the couplers (to connect the drive screw to the stepper), and the anti-backlash nut. The latter we have already discussed, the former I solved by biting the bullet and buying some Lovejoy jaw couplers. You can use rubber tubing to do the coupling but eventually you will want to go to the better type of coupling. If you decide on Lovejoy couplers (or similar) you will almost certainly find you will have to import them from the US- they ARE available in Australia but when I researched them they were about 5-6 times the price of the same item in the US. Alas,, shipping prevents them being very cheap ($10 each in the US) but it's still better than to give money to the robbing bastards here.



Yes Coupling motor to thread has come to mind as well i have looked into it but since i don't have any motors yet apart from what i was thinking of using at the start its a problem that will have to wait till i know what i am doing here .

I was looking at making them my self again cost cutting ,i have seen the tube of rubber or plastic tubing used i think i can make some thing better but if ebay sales are kind to me i will look into those nice couplings.
Yes we do get ripped off here whats for sale over seas ,thats a nice thing about ebay for us .
But anycase i will look into them if i can .

Do NOT be tempted to buy those couplings from Jaycar - they are way overpriced and not suitable for this application.


Oh i didn't know they sold any ! my hope was work it out old trial and error make and see.

NOTE! It is essential that the coupling prevents any significant sideways (lateral) forces from reaching the stepper otherwise the steppers will not last long. All of the lateral force should be absorbed by the bearings either end of the drive screw - ideally these would be thrust bearings but skate bearings seem to do well and are very cheap and readily obtainable.


I do have bearings either end for the thread i can see if i was just using the stepper motor would not be a good idea it sounds like the coupling should give a little if i am right in saying .

Is this guys idea what you mean Gary

http://www.youtube.com/watch?v=99q_1xiZcrE
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Postby Harry Dalek » Sun Feb 17, 2013 8:39 pm

I was thinking more of this idea when i started.

http://www.youtube.com/watch?v=i0sTrSkoDs0
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Postby gary » Sun Feb 17, 2013 8:41 pm

well in regard to anti-backlash - yes - but there are a huge number of solutions to the problem but as I said an all-thread coupling nut has been sufficient for me and much simpler than most solutions.

Do you know what I mean by an all-thread coupling nut? If not I can post a picture.
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Postby gary » Sun Feb 17, 2013 8:44 pm

harry dalek wrote:I was thinking more of this idea when i started.

http://www.youtube.com/watch?v=i0sTrSkoDs0


NO! there is no give in that kind of coupler so you are in danger of having it bind or seize if there is any movement at all in the drive screw - if you can achieve that then it will work - I know I couldn't.


BTW THAT is the kind of coupling nut I refer to as the anti-backlash nut.
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Postby Harry Dalek » Sun Feb 17, 2013 9:33 pm

Gary am i right in saying if that last you tube guy used a bearing and that all-thread coupling nut that would of been better for anti back lash doesn't look like he used one.

Did your all-thread coupling nut fit the stepper and thread ...did you put a thread on the stepper ?
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby gary » Sun Feb 17, 2013 9:58 pm

I am not sure Harry but I think you have things completely around the wrong way. I didn't use a coupling nut as a coupler - I used it as an anti-backlash nut. That is the nut that moves along the drive screw (all-thread rod) and is attached to the gantry (and z axis carriage).

They are called coupling nuts because they are used to couple 2 lengths of all-thread together. In our CNC case they are not being used that way - they are being used because their long length reduces the amount of backlash it has along the all-thread (i.e. that bit of movement you can feel with a normal nut on the all-thread).


The coupler I am talking about (as opposed to the above) is the thing that connects the stepper to the all-thread - that requires some "give" because the stepper is solidly fixed and so is the all-thread once mounted on the bearing - and they might not exactly align causing lateral stresses on the bearing of the stepper which is not designed to take that.

If that is not clear I will have to post a diagram or picture.
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