Looks like a valve build might be able to happen this weekend! We are pumped to get the Ion firing more effectively. As long as I can get to work on some design we should be able to turn it out this coming weekend!
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With our last build resulting in a gun that could be muzzle loaded to fire single shots, Brian was confident that we could attain semi-auto firing over the course of the coming weekend. The main problems and parts that needed to be addressed to get to that point were correcting the cycling issues in the bolt, rigging a sort of makeshift trigger system to fire the gun, and feeding paintballs into the system.
The issue that had to be solved first was the issue of cycling. After our second build, we found that the bolt was not being forced forward by the firing pressure when the control pressure was released. To fire the gun, we had to assist the bolt by pushing on the back of it with something. We expected that the primary cause of this problematic friction was the surface finish of our internal parts. This appeared to be an easy fix after some fine grit sanding on the lathe. Another way that we helped the movement of the bolt was by deepening the o-ring grooves to relieve a little pressure on the bolt.
After these two fixes, the bolt started to cycle the way it was intended. In order to achieve semi-automatic dryfiring, we had to rig up a hose system to imitate our future trigger. This is roughly what we came up with…
In this setup, pressure is supplied by separate hoses. The firing pressure is constant as it will be on the final version, and an air gun is used to dump pressure from the control chamber in place of a solenoid-actuated valve. We did have a problem off the start because the trigger pressure input was pumping air too fast for the air gun to dump it. this was causing the chamber to remain at too high a pressure for the bolt to cycle. to fix this, we basically jammed a plug into the input hose to slow the rate at which air could flow through it just enough to allow the bolt to cycle. With this setup, we achieved semiautomatic fire without ammunition.
At this point I am returning to this post after over a year of absence, so my recollection may be a bit fuzzy. I apologize for any inconvenience.
In order to feed paintballs into the gun, we decided to create a basic hopper feed system by boring a large hole in the top of the gun. We then threaded the hole and created another piece that fit tightly onto the neck of a hopper and threaded into place on the gun.
Since this was the first time we had to do anything on a different axis than the firing axis, it meant we got to use a new toy. Brian had recently bought a four jaw chuck that was useful for this type of operation. The mount for this job is pictured below. The hole was started using a wood bore bit, and the hole was widened using a boring bar.
After making both parts, we attached a hopper and voila! It is amazing how much that hopper makes it look like a gun.
We rigged up our makeshift trigger system (partially pictured above) and took it outside to try firing it a few times.
Now that the firing mechanism is operational, we need to set up a trigger mechanism. The primary phase of this process will be the design of the solenoid valve. A concept is shown below.
First: A cross-section of the valve Second: A full image of the valve hammer
This valve will be actuated like a solenoid. There will be a copper wire winding around the left end of the valve body which will pull the hammer back when charged.
In the rest state, pressure will be routed through the valve as such:
With the valve in its rest state, constant pressure is applied to both the control chamber and the firing chamber. Due to the pressure in the control chamber, the gun does not fire. Once the valve is actuated by an electric current through the solenoid, the air pressure will behave as such:
With the control pressure now dumped, the present firing pressure will be able to fire the weapon. After firing, the source pressure will return the hammer to its original position as soon as the solenoid is deactivated, allowing the recharge of the control chamber.
Hopefully with some refinements to this design, and a free weekend to build, Brian and I can get a real paintball gun together. We still have to deal with making the gun run on CO2, which brings in a whole host of regulation and expansion issues, but I think we are fairly close to a workable product.
I am sorry to anyone who was affected by my delay in posting this write-up, and I hope you enjoy its contents.
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The most recent success in my ongoing RF-45 mill repair project is the fabrication of a new Y-Axis lead nut. The stock nut was apparently lost somewhere along the way during the attempted CNC conversion that I’m partially reversing, so I had to come up with a replacement.
My first thought at replacing the nut was to make a new one out of acetal plastic based on the method described at the Home Shop Machinist Forum. On second thought, I decided it would be much more practical to see if I could find a replacement part online. Like many of the chinese machine tools out there, this mill is one of many clones of an original design. In this case, the Rong-Fu 45 is the original, and my copy was produced by Penn Tools. Unfortunately, I was unable to find replacement parts through them, but Grizzly sells a similar mill along with replacement parts. I dug through the manual to find the part number, contacted Grizzly, and ordered the nut. Easy enough right?
Unfortunately, the importer of my mill chose to use 8 TPI leadscrews, while the Grizzly version uses 10 TPI leadscrews, so the nut didn’t work. I returned it to Grizzly, and set off on my original plan of making the nut from scratch.
I started by boring and splitting the acetal to fit the lead screw:
After getting the simple 555 based MC-2100 driver circuit working, we moved on to a controller with more features. I’d been looking for an excuse to make an arduino-compatible board (here’s a description if you’re not familiar), and this seemed like the ticket.
The initial spec for the controller included the following functions:
- Read user input from potentiometer
- Send the 50ms period PWM signal to the MC-2100
- Sense the lathe’s spindle speed using a magnetic reed switch or equivalent
- Display the spindle speed on a 7 segment LED display
At this point, the controller meets the requirements laid out above. I’ll discuss the implementation of each feature into the controller in the order listed above.
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After discussion with Terry in the comments of previous posts, we came to the conclusion that the MC-2100 wasn’t expecting a full 5V signal at the control signal input (blue wire). As shown in the MC-2100 schematic, the optoisolator on the input (U1) has a 22ohm resistor (R2) in series with it. Applying 5V to the blue wire results in 170mA flowing through the optoisolator, higher than its 50mA rating.
This lead to the conclusion that there must be another resistor in the circuit at the dash panel end of the blue wire. Upon inspection, there is a 240ohm resistor in series with the control signal output on the treadmill’s dash panel PCB. With the series resistance at 262ohms, the current through U1 is now 15mA, a much better current level for reliable operation.
Taking things a step further, it’s possible for the circuit to operate on higher voltage if a larger series resistor is used. This allows us to eliminate the 5V regulator from the circuit, as well as the transistor from the output, which was mistakenly added to allow the higher output current the circuit required without the current limiting resistor.
Here’s the resulting circuit (keep reading, not done yet!):
Following the first day of work, we had nearly completed both the bolt and the charge chamber, and had completed the boltstop. In this session we needed to finish up these parts and create the firing chamber. Brian and I had high hopes going in to this session. He was confident that we would at least fire a shot by the time I had to head home. I was somewhat skeptical! Although we were interrupted by some thermite and Doctor Mario, we were able to achieve this goal.
We did the usual shaping and machining to get the firing chamber roughed out and then got on to the fun stuff… threading. Three parts needed threads. The firing chamber and charge chamber had to thread together at the middle of the gun; and we had to thread the inside of the front end of the firing chamber in order to put one of our Spyder barrels into it. The charge/firing chamber threads would be somewhat simple, as they only have to match each other and require no standardized dimensions. The barrel, on the other hand, has its own thread type that we would have to match. Just to make things more fun, The threads were metric, (M22 x 1.5) and our thread turning gears were standard. Brian worked his magic and got something pretty close to the barrel (7/8 x 16) and we went with it.
External Firing Chamber Threads
Internal Barrel Threads
Whole Firing Chamber
And I have saved the internal threads from the charge chamber for last to present you with a conversation that took place just moments prior to the cutting of the first internal threads we had done.
Joe and I: “Brian are you sure you want to do this without a practice run or anything?”
Brian: “I know what I am doing.”
He apparently wanted our threads to look like the mouth of the Kraken, but as long as he knew what he was doing, who were we to question him! 🙂
The embedded video shows our first paintball break on target.
The graphic above shows the air system we had set up when we fired the gun. Constant pressure is supplied to the firing pressure input, where the pressurized air waits to be released and force the ball from the gun. The bolt is held back by air pressure from the trigger pressure input. Whenever the air gun valve is open, this pressure is supposed to be keeping the bolt to the rear and keeping the gun from firing. Whenever this pressure is released (the air gun is pulled away from the input) the firing pressure should cause the bolt to move forward and the gun should fire. This wasn’t happening for us due to what we speculate to be general surface finish and O-ring fitting issues. With some further work and refinement this should be fixable. We ended up poking the back end of the bolt with random stuff and that provided the motivation required to start the firing cycle.
In response to Terry’s comment on my previous MC-2100 post, I got the breadboard circuit hooked back up for some testing. In doing so, I found a couple things missing in my previous schematic. I also may be backing off calling this version of the circuit done. It looks like there may still be a bit to learn :).
This is another quick update on the MC-2100 PWM controller project. I’ve tweaked the schematic a bit to put the 5v regulator at the beginning of the circuit, which I think is a better configuration. This circuit is currently on a breadboard, and worked great until the connections in the breadboard started wearing out (around a month of occasional use, including our paintball gun build day). Here’s the latest (and probably final) revision:
When I started this project, I wanted to get this circuit working without a microcontroller for the sake of education and simplicity. At this point, I’m comfortable with calling that goal achieved. Now it’s time to move on to more features, like a tachometer and possibly closed loop control!
My current direction with this project is to develop a combined tachometer/speed control for the MC-2100 and my lathe. I plan to use an arduino to measure speed, display the speed via 4 digit 7 Segment modules (salvaged from the treadmill control panel), and send the PWM signal to the MC-2100. At this point, Joe and I have a working version of the code put together, and the circuit prototyped on a breadboard. I’ll update with progress once we’ve got something more final.
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Once Brian had gotten his design work fairly completed, we knew it was time to dive in and start our construction. I got a free weekend and headed up to Brian’s for a long day of trial, and hopefully not too much error!
We decided to start work on the smallest and most simple part to sort of “get our gears turning” on the lathe. 😉 This part was the bolt stop, as shown in the picture below and depicted in yellow in the previously posted CAD screenshots. We somehow proceeded to pull it off without a hitch and moved on to some more “interesting” parts.
Ben came over for the weekend a couple of months ago, and we were looking for a project to do in my fledgling machine shop. He’d never really used machine tools, and I hadn’t done any “real” machining in my home shop yet, so we were looking for an excuse to pick up some experience. Ben’s in to paintball, so we decided to try to make a paintball gun.
We tossed around making a Spyder clone since that’s what Ben’s taken apart the most, but decided not to because I wasn’t sure how we could make the stacked tube housing with the tools currently in my shop. Keeping things to a single centerline makes them a lot easier to make on a lathe!
The next type of gun that came to mind was the Tippman style marker. They work on basically the same principle as the Spyder, but are arranged in a straight line rather than two stacked tubes. However, neither of us had ever owned a Tippman, so we couldn’t just make up the design from memory. We did a bit of research and came across a great site in ZDSPB.com. With the info on that site, and a few crude hand sketches, we headed out to the shop to “get something done.”
Just a quick update. I haven’t finished the permanent driver board, but thought I’d upload a better version of the schematic. I’m currently trying to decide if I’ve messed up the MC-2100, or if my soldering just sucks. At this point, I’m getting the motor to come on, but not consistently like it was with my breadboarded circuit. The indicator LED will flash 5 or six times, and the motor starts turning, then the LED goes back solid like it’s not getting signal, and the motor slows back down. I’ve had a couple of occasions where the motor will run up to full speed, so it’s at least close. I can at least confirm that this circuit worked on the breadboard, as shown in the previous post.
I also wanted to post a few of the relevant files I’ve found pertaining to the MC2100.
Here’s the document that describes how the controller is interfaced with the treadmill, and the function of each pin of HD2 on the MC2100. This is essentially the same file that James linked to in the comments on my previous post.
The following file has been extremely helpful in troubleshooting the MC2100 itself as I’ve messed it up along the way. The file was provided by a member of the Home Shop Machinist forums in this thread.
Free treadmills from Craigslist are a great source of DC motors and motor controllers for machine tools. A quick search will yield several examples of people repurposing these motors and drive for drill presses, lathes, and various other equipment.
From what I’ve seen, the MC-60 type controller is by far the most common in low end treadmills (the type you typically can get for free). Three out of the four treadmills that have passed through my garage have had the same MC-60 controller, and nearly identical permanent magnet DC motors. This controller is relatively easily repuroposed as a machine tool drive, as the input is a simple voltage divider circuit driven by a potentiometer. Just take the pot off the treadmill’s dash, mount it to your bench, and you’re up and running.
The MC-2100 proved to be a bit more complicated. My first clue was the all digital dash on the treadmill it came out of. A quick google concluded that the MC-2100 required a 5v PWM signal with ~50ms period. I found a good reference circuit on the All About Circuits forum (Link):
This circuit has two stages. The first is an astable 555 vibrator. Tapping off the capacitor charge pin (Pin 6 on the 555) results in a sawtooth output, with the frequency set by R1, R2, and C. This sawtooth is then fed into a LM393 voltage comparator to convert the sawtooth wave into a square wave.
Here’s my final circuit sketch:
And a quick first test video:
In my opinion, it was worth the effort to figure out because the MC-2100 is a high frequency PWM controller, as opposed to the MC-60 which is an SCR based controller that operates at line frequency. This results in a much quieter motor. Also, based on a couple quick test cuts, the MC-2100 seems to have a higher current capacity.
I bought an old Atlas lathe on craigslist last year for $50. It was in need of a good cleaning and was missing a few parts, but all in all fairly sound. Joe made a replacement tailstock ram for it, and I’ve bought a new chuck and toolpost, and a few other bits. All in all it’s working pretty well after about six months of working on it off and on.
One of the last features left to get working was the power cross feed. On this lathe, the cross feed is driven through a bevel gear set. The drive gear slides over the lead screw, and is supposed to be driven by a key that engages a slot in the lead screw. The bevel gears are ZAMAK castings, and the key appears to have worn away or broken years ago.