# I Need An Opinion Or Three



## davidh (Oct 14, 2015)

i have painstakingly built and assembled the gantry assembly as shown, not I'm into ball screws and bushings and need an opinion or two.  i have made Delrin bushings that press into the holes that are machined into each end of the "X" & "Y" locations, and carefully turned and bored these bushings to fit nicely.  the bore on them is +.001-.002 and they feel good on the ball screw shafts.  what ramifications would there be if they were say +.003  +.005 or even a bit more, when the motors turn either direction quickly ? 
the motors are or will be direct coupled to the screws with aluminum semi flex couplings and set screws to keep them secured.  maybe roll pins should be added also ?   I'm to the point where i will install them and really don't want to re-do any more than i already have.  thanks in advance.


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## REdington (Oct 14, 2015)

Delrin will work for just a bushing for the ball screw to ride in and +.005" will work.  I'm guessing that the screws will ride in these bushing in one end and you'll have thrust bearing with preload on the other.
BTW nice start on the router.


 Rodney


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## JimDawson (Oct 14, 2015)

REdington said:


> Delrin will work for just a bushing for the ball screw to ride in and +.005" will work.  I'm guessing that the screws will ride in these bushing in one end and you'll have thrust bearing with preload on the other.
> BTW nice start on the router.
> 
> 
> Rodney



:+1:

As long as the lead screw is held securely in the bearings, I don't think there is a problem with the Delrin bushings. 

A roll pin should not be needed even with the set screw type.  The clamp type flex couplings hold better than the set screw type.  



Putting a small divot in the shaft under the set screw is helpful.
.


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## davidh (Oct 14, 2015)

thank you, and thank you.  i wa intending to use delrin for the thrust bushings also, then i considered doing some internal threading that will match the threads on the ball screws.  a lot of screwing around but another test of my abilities.  trying to explain here, an internal threaded thrust nut, made of delrin, against a nice flat washer thats the same delrin, locked in place with a clamping set collar made of mild steel.    i will halve to count the threads on the ball screw again and make a tool profile that will just cut like glass.  that delrin is some great stuff to work with, so far anyway.    i've already cut the lock nuts for the 15/16 threaded ball screw (nut ? ) and double nutted, that should secure the thing to the gadget.    im running out of names to call them.  anyway, that was an interesting project too, i had a box of nice plated hex nuts so i bored and threaded them, then parted them into two pieces,  andthey seem to fit quite nice.


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## countryguy (Oct 14, 2015)

I loved those flex couplings.... Of course - automation direct!   Jim turned me onto them.   I  also am a teacher in IT so I called them up - they have an Education discount.  15%.   Are you a student of something?  They just need a .edu email if I recall.     LOVE those guys.  
CG


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## chevydyl (Nov 10, 2015)

My favorite coupling is a Ruland Oldham type, zero backlash, with a replaceable disc when it wears out, they handle large amount of misalignment. Like for instance when your screw isn't aligned perfectly with your motor, the disc slides between the couplers...


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## davidh (Nov 10, 2015)

I MAY NEED THOSE kind of couplings,  in order to get all this stuff aligned proper, a guy should have saved all the "x"-"y"-"z" shaft bores for a line boring machine,  cheeze and rice, i keep making things over and over and realigning and, well you that have crossed this bridge, must know.
12 more holes to drill and tap for the "z" rails (second time, second piece) and i shoul dbe able to mount the motors and turn the shafts by hand.   then another thing caught my eye:  my motors do not have thru shafts (hindsite is 20/20) how does one get all the axis's to zero zero zero as a starting point?  do i need to add on to the ball shafts so i can install a large knob or crank or ? ? ? ? 
and qnother question for you that have done this:  what do you use for the wires that must flex continously ?  the "x" is ok, but "y" & "z" will constantly be bending. 
im getting closer and closer to the fun part...  thanks for the advice so far.


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## chevydyl (Nov 10, 2015)

Home switches will handle 000, then you will have to program an offset if you place the part in the center or wherever.
I don't have homes on mine so I have to find every edge and zero each axis in Mach for my part zeros, if I did have them I could place my stock against a stop, like the edge of my vise and just hit go (IF offset is programmed and predetermined)
Sorry not EVERY edge just my x and y
You can add manual pulse generator wheels and move the axis individually too.


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## TomS (Nov 10, 2015)

I used double diaphragm type couplings, like the one pictured below, on my CNC conversion.  Oldham couplings are good as well.  This is another option for you.

Tom S


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## davidh (Nov 10, 2015)

i looked up the oldham couplings,  they must be gold plated, based on the prices.  maybe i read it wrong but looked to me near $100 each.  whew !
who makes or supplies the double diaphram ones ?


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## chevydyl (Nov 10, 2015)

you want Ruland branded, I paid like $25 each for mine, go to there site and find a local distributor
I spoke with a Ruland rep, HAAS uses a rigid coupler made by Ruland, they are US made parts

I just looked up a half inch shaft coupling, 40 bucks, mine were cheaper as I had 1/4in shafts

one last edit,  personally I would use US parts, better manufacturing tolerance, ZERO backlash, plus you can always get replacement discs


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## TomS (Nov 10, 2015)

davidh said:


> i looked up the oldham couplings,  they must be gold plated, based on the prices.  maybe i read it wrong but looked to me near $100 each.  whew !
> who makes or supplies the double diaphram ones ?



I bought my double diaphragm couplings on eBay.  IIRC about $25 each with free shipping.  EBay should have Oldham couplings for a reasonable price.

Tom S


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