Constructing Janus, by Dirk

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Re: Constructing Janus, by Dirk

Postby dirktheeng » Sun May 08, 2011 8:54 pm

bdring wrote:No, there is no warranty. Actually there is an anti warranty. If you destroy something while trying to void the warranty there is a warranty. In other words, I'll gladly support innovative hacking gone bad with replacement parts. :D

My motto "If you didn't build it, you will never own it." is a hack on the "Makers Manifesto"... If you can't open it, you don't own it. I read "open it" as "hack it"

http://makezine.com/04/ownyourown/

Good work Dirk. I actually have a few similar things in the works to release if and when MakeSlide is available.

PS: Z pulleys do go underneath per the drawing.



Thanks Bart. I actually saw I had room to do that while I was sitting and writing the last post and switched it up inbetween writing that last post and when I saw yours. BTW what is MakeSlide?
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Minimizing and/or eliminating slop in idler bearings

Postby dirktheeng » Sun May 08, 2011 9:41 pm

When I assembled the gantry and tested the motion for the first time, I was a bit dissapointed because it seemed to be somewhat jerky. Something wasn't quite right. After playing around with some things I found the cause. It seems the nylon nuts were not sitting quite square to the 1/4-20 pan head bolts used as the shafts of the idler pulley assemblies. This caused the shaft not to sit quite in a co-axial arrangement with the bearings which was causing the pulley to wobble. Further, the pulley bore doesn't quite match the OD of the threads of the bolt, so when the set screw is put in, it pushes the pulley off center. In other machines I have built, the shaft colars are about 0.001- 0.002" larger than the shaft and would fit very snugly (almost hard to get on sometimes). If they were at all loose, I would just touch the shaft with some sand paper to raise some burs. I once cut a shaft much to small that was very important and the machinist helped me fix it by carefully knurling the surface to make the part snug again. Well, not having that, I thought about what I had around the house to bring up the OD of the threads. What I found that worked very well was masking tape. I carefully cut a single layer of masking tape to fit around the shaft. It brought the OD up to the point where it took a bit of effort to push the bolt through the center fo the bearings. It stays on its own without any need for a retaining nut. It actually takes some doing to get it out. It does not seem to move when in operation even if the pulley is far away from the bearing. This also did the trick to keep the pulley concentric.

There is now almost no wobble in the idler pulley. The only way we are going to get better is by replacing the bolt with a ground shaft and locking collars, which I may do someday. I am concerned that the threads will end up cutting through the tape over time, thus loosing the shimming affect and introducing wobble again. It is important for the axis to move smoothly because these steppers are small and on fast rapids they could miss stepps if the wobble is particularly bad. Upgrading to a ground shaft with lock colars wouldn't be very expensive. I would be surprised if the whole thing would cost more than $10.

Here is a photo of the assembled arrangement.

DSCN3378.JPG
Tape Shimming idler pulley


Sorry, the photo is a bit out of focus, but you can see a slight line in the tape. That is actually where I cut the tape so that there isn't overlap. I will keep you posted how this solution works out over time. I have my doubts about the tape holdin it's own, but we'll see. Let me know if you have any other ideas.
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Janus gets dressed up with a lid and a table

Postby dirktheeng » Mon May 09, 2011 12:30 am

Got the table and lid assembled and put on. It is not aligned yet, but it works very well. The table moves very freely. Here's a couple pictures.

DSCN3379.JPG
Lid open


DSCN3380.JPG
Lid closed
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One important note about expanding the x axis to 13"

Postby dirktheeng » Mon May 09, 2011 12:34 am

One thing I forgot to mention was that expanding the x axis travel was that it necessitates using a z-axis motor as you cannot access the threaded rods or the belt easily without the skins being off. That isn't a big impediment to most of us though as we plan to use a z axis motor anyhow.
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Re: Constructing Janus, by Dirk

Postby twehr » Mon May 09, 2011 12:16 pm

Dirk,

I think you are actually expanding the Y axis, not the x.

Anxious to see all the things you did to change this.
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Re: Constructing Janus, by Dirk

Postby mlconti » Mon May 09, 2011 4:09 pm

Dirk,

I noticed you installed an extra angle bracket where the "control" panel goes in the front, was that intentional?

Looks good!!!

Mike
If you can think of it, I can Automate it!
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Re: Constructing Janus, by Dirk

Postby dirktheeng » Mon May 09, 2011 8:32 pm

twehr wrote:Dirk,

I think you are actually expanding the Y axis, not the x.

Anxious to see all the things you did to change this.



Which ever axis moves the entire gantry is the one I mean.
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Re: Constructing Janus, by Dirk

Postby dirktheeng » Mon May 09, 2011 8:41 pm

mlconti wrote:Dirk,

I noticed you installed an extra angle bracket where the "control" panel goes in the front, was that intentional?

Looks good!!!

Mike


Yea that was intentional. It isn't an extra one, but I moved the bracket from pointing to the back to pointing to the RHS to allow me to move the cover trip switch over farther out of the way. I don't think it will cause a problem with the pannel, but I will have to see. Nice eye though
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Precision shafting replacement

Postby dirktheeng » Mon May 09, 2011 10:00 pm

I’m not sure how the tape fix of the wobble is going to work out in the long run so I wanted to see what it would cost to upgrade all the shafts in the whole build. Here’s what I came up with

From McMaster
95606A120 – nylon washer, 0.38 OD, 0.25 ID, 0.02 thick pack of 100, $5.05, qty 1
1257K67 – ¼” miniature drive shaft, 18” long, $9.64 each, qty 2
9414T6 – plane Jane black oxide ¼” set screw shaft collar, $0.60 each, qty 4

From Missumi

CPF16-5-6.35 – 5mm to ¼” sleeved style shaft coupling, $8.00 each, qty 2

Total price $42.73 plus shipping. That’s not bad for replacing all the shaft with precision products.

The idea is to get 1 Y axis drive shaft (12”) and 2 idler shafts out of each 18” shaft from McMaster. I will use the shaft collars to hold the back of the idlers in place and the existing pulleys in front with nylon washers to add space if necessary.

I want to check with Missumi about any backlash in the coupler before I order.
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Re: Constructing Janus, by Dirk

Postby bdring » Mon May 09, 2011 10:13 pm

Be aware that all R4ZZ 1/4" bearings are not exactly 0.250" I.D.. They are actually 0.2465 I.D. When you see fractions used for bearings you need to check the actual size. That holds true for a lot of things like pipe, conduit etc. Blame our English measurement system. Precision 0.250 shafting will not fit.
Bart
"If you didn't build it, you will never own it."
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