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Show and Tell Scribe Attachments DIY or Bought

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plasmartist
Posts: 39
Joined: Mon Aug 07, 2017 1:31 pm

Show and Tell Scribe Attachments DIY or Bought

Postby plasmartist » Mon Sep 18, 2017 2:32 pm

Hey guys, I have attached some pictures of a cnc scribe that I pieced together and built. While it is functional, I still don't absolutely love it and I would really like to see what others have built or bought, along with references. I do not own a mill, so my aluminum brackets are backwoods machined on a drill press, there are many short comings to the way I built mine, however the aspects I do like are the way I plumbed the solenoids and controls. But the linear thruster itself is my biggest problem.

Parts sourced:
Linear thrusters: sourced on ebay as an assortment of various used thrusters $145 for 6 (half were unusable for this with too much slop in the bearing)
pneumatic solenoids: sourced on ebay cheap chinese about $15 each
push to connect fittings: Bought a few assortment packs, probably a total of $50 amazon and ebay
8mm air tubing: Amazon $15
Chigago Pneumatic 9361 scribe: amazon for $273
air regulators and oiler and 1/4" fittings: harbor freight roughly $75

Concept:
Air in at regulator/dryer combo and reduce to 100 psi.
(Keep in mind the plumbing is made based on what fittings I had at the time)

One side of the 1st T goes to the Scribe side via a 90psi reduction, then a 3 way 2 position solenoid, and finally an oiler.

On the other side of the T I added one more T to split my up and down operation bc they use different psi. For the UP I am running about 30PSI through a 5 way 2 position with port B plugged, i.e. no current = port A open and port B closed, opposite is true when there is current. (disclaimer, I'm far from an expert, but I knew this would work so it's the route I took).
On the other side of the 2nd T is the DOWN Air Solenoid using a 3 way 2 position
solenoid with about 7-10 psi. (the up and down use different PSI because one is lifting
while the other is dropping.

As for the Linear thruster:
Half of the thrusters I received in my bargain combo pack had fairly worn linear bearings, so despite them functioning in general, they would be too sloppy with lateral forces. Thus you see I am using a very large thruster because it had the tightest bearings. Rigged up a few brackets from scrap aluminum blocks from a machine shop bin.

To hold the scribe I drilled a vertical hole in one black, then did a lot of whittling with a cuttoff wheel and dremel to make it usable. Basically the same process for my other brackets.

Downfalls:
While this works as a scribe, and functions, there are many downfalls. First off, the linear thruster is first off probably too large for this application and secondly too worn to function consistently at lower PSI. One thing I have had a problem with is my DOWN function, sometimes 7 PSI isn't enough to make it down so I have to run at 10 PSI, however at 10 PSI the pressure on the scribe can be excessive causing too much lateral force and make the scribe bind and hop. I'm thinking that using a smaller bore piston thruster will allow higher PSI and be a little more precise without creating too much force.

Another downfall to this design is that since my scribe runs independent of the Z axis, every start and finish of a marking requires traveling 3 inches up and down, and with how big it's built it feels like i'm really slamming that scribe around. For my next one, I want to switch to a velox z axis and mound the thruster to the z axis. This would allow for me to shorten my thruster travel to about 1", furthermore, during the scribing operation I could have the thruster and scribe engaged for the entire operation and use the z for lifting and lowering the scribe. I feel this would have much smoother operation. I don't know what settings to use in sheetcam yet, but I saw a youtube video of one set up like that and it seemed super smooth.


Again, please share the way you built yours. I am wanting to completely rebuild mine, or possibly buy a prebuilt thruster designed for the cp scribe. In fact, I'm not terribly fond of my ppllc z axis, so will be replacing it soon and would be interested in a completely integrated z axis and scribe setup.

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