Sunday, June 25, 2006

X1 Flood Cooling

It has been a while since my last post, but that's cuz I've been a busy little basement engineer! :-) I built an enclosure for the mill and implemented a flood cooling system. In addition to the cooling and lubrication benefits of a flood system, it is nice to keep the chips contained to a controlled area.

Basically it is an enclosure made from 3/4" MDF sitting on a base made of 2x4's.




What spurred me onto this was, while trying to make my pulleys, I discovered that the slow feed rates necessary with my ad hoc belt drive caused the 2024 aluminum to almost flake off. Airborne high strength aluminum dust can't be good! So, to solve that problem (plus gain other benefits) I built the enclosure.

The bottom is lined with 1/8" thick rubber that can be had from McMaster-Carr, 4 ft worth of P/N 86795K43. The filter setup is a food storage container with the bottom perforated, a large hole cut in the top and some nylon mesh sandwiched between the top and bottom for filtration. The mesh is also from McMaster (9318T48) and has .002" openings. It is about 40% open so flow isn't an issue. It doesn't let any solids past! The only issue I've found is that the coolant I'm using has a bit of a tendancy to foam, and that doesn't drain so well. I turned down the flow on my pump a bit and that took care of the problem for the most part. Speaking of which, the pump if from Harbor Freight, their P/N 45305.

I'm very pleased with the enclosure, and an unexpected benefit is that the 3/4" MDF really cuts down on the noise, which makes my wife happy! Most of the noise comes through the large front acrylic doors, but the ear protection knocks that down the rest of the way. Mainly it is nice that it keeps the noise polution out of the rest of the house.

I finished up the spindle pulley yesterday and will be working on the motor pulley today. I haven't test fitted the pulley yet, but if my calipers are accurate it should fit nicely!

BTW, the motor that I'm using is a 2.5 peak HP unit from Surplus Center.  Two things: they don't sell the correct speed controller for it and, if you work it hard, it will need a fan. 

All the DC speed controllers Surplus Center sells (currently) are of the SCR variety.  This motor is PWM rated.  Running it off a SCR controller will make it hot very fast, can fry the brushes and demagnetize the permant magnets.  Unfortunately, about the only PWM drive I've found that is rated to run this cheeta of motors is the KBWT-112 from KB Electronics.  It can be purchased through solidstatedrives.com.  It ain't cheap.  I'm getting away with running it on an SCR controller, but I've got a fan on it and try not to load it too hard.  The motor has a thermal switch (which can be wired in series with the armature wires) which will open at about 100 degrees C.  Having the motor abruptly shut down in the middle of a toolpath is frustrating, but the steppers will just get angry and it is better than smoking the motor.  The KB drive is definitely in my near future.

Speaking of the fan, with just a little creativity this is an easy thing to accomplish.  If you look closely at one of the pictures in the New Enclosure gallery at the right you'll see the fan... just look for the shiny propeller whizzing around at about 5000 RPM on top of the motor.  It is a 1/2" wide, 1/8" thick piece of aluminum stock.  I drilled a 9/32" hole at the exact center, put it in the bench vise and twisted a pitch on both sides.  I pressed (lightly hammered) it onto the stubby shaft coming out the top of that motor and VIOLA!  The motor now has a fan!

Ok, some might call that crazy to have an unshrouded "fan" whizzing around like that but keep in mind it is behind .220" thick acrylic.  There's no way I'd try this trick if it were just out in the open.  I've ran it for probably about an hour or two total now and it works great.  The air inside the enclosure is noticably warm when I open the doors after a long milling job so it is definitely cooling the motor.

Thursday, March 2, 2006

X1 Counterweight Installed

The counterweight is installed! It was pretty easy as a novice such as myself did it in about an hour. I think the longest part of the project was going very slowly with my new tap and die set to make sure I didn't break anything.




Tuesday, February 28, 2006

X1 Mill Head Counterweight

It is somewhat commonly accepted that the head of the Micro Mill needs to be counter weighted so that the Z-axis screw isn't doing all the "heavy lifting." One thing that I found interesting though is the amount of folks on the 'net that will simply quote a McMaster-Carr part number for a gas spring or state that they are using a pulley system of some kind. I have yet to find someone that backs up their counterweight system with some empirical research. Also, I've seen folks using gas springs that are significantly longer than the mill's Z-axis. What's that about? I've also seen some very elaborate mounting systems to compensate for "out of square mounting surfaces" and the like. There's basically some pretty poor engineering going on out there. Scratch that! Some of this stuff should just be common sense.

So that other folks can benefit from my research and draw their own conclusions rather than simply accept mine, here's my counterweight narrative:

I just took a rough measurement of the head weight. This method won't work for everyone, and the "why" will become evident quickly! In order to measure the head weight after it was mounted on my bench, I had to get creative. Yes, I could have just yanked the whole head off and placed it on a scale, but there are a few problems with that. First, it is awkward and hard to get an accurate measure on bathroom scale. Also, it has a light covering of oil on various surfaces and I hesitate to slime the scale. Most importantly, I'm lazy and would rather not have to try to remount the head after removing it!!

The solution was to start by locking down the Z-axis using the gib screw. I then unbolted the Z bearing block. After placing a bathroom scale on the floor, I had my wife climb on and I took the reading. Not everyone's wife would be that accepting as being used as an instrument of measure, but one uses the tools at his disposal! Kudos to my wife for being a good sport! Anyway, I unlocked the gib screw and, after making sure the head moved up and down freely, took another reading. We moved it a few times and took further readings just to verify. After some cowboy-style statistical sampling, I figured it was a good enough data set. I locked the gib screw and sent my wife off to wash her hands!

The total weight of the head is 19.5 lbs. Frankly, I was really hoping it would be closer to 25 lbs so that I could use a 30 lb gas spring and get 5 lbs of upward preload to deal with some of the lash in the Z screw. I think I'm going to go for the 20 lb gas spring, thereby achieving almost a neutral weight and deal with the backlash in a more appropriate fashion at a later date. But wait: "surely you can find a 25 lb spring" you say. And to that I would answer, "yes, I can" but more important than further pursuing this inappropriate backlash fix, I have other reason for choosing a 20 lb spring.

I'm sourcing the majority of the hardware for this project from McMaster-Carr. Mainly due to the fact my local hardware stores suck. The ones that are open past 5pm just don't have a good selection (and I refuse to shop somewhere that closes their doors before most folks get home from work). McMaster is also cheaper in many cases. They are also excellent folks to deal with, ship quickly and provide one stop hardware shopping. These and other reasons have directed me to choose to limit myself to their selection. Of the gas springs they offer, the smallest available in a 25 lb size is 18 inches long fully extended and over 10 inches compressed. Not a truly good fit for what I'm going to do with regards to mounting.

This brings me to another design upgrade this project offers. Without having the Z gib very tight, the front of the head sags slightly. Not ideal when trying to plunge and end mill or do precision boring. To help with this the ideal solution is to get the counterweight force as close to directly below the center of gravity as possible. Anyone know where that is? I can certainly tell you where it isn't! At the lead screw, screw bracket/nut, or gib! Right where most gas springs are mounted! This is where the folks using pulley systems really have the design advantage. They can choose a mount point in a number of locations. I would do a pulley system, but they look gangly. :-)

The final solution (all part numbers are from McMaster-Carr):

Part Number
Description
9416K171
20lb M6 threaded end gas spring
9416K74 (2) 10mm steel ball sockets for M6 threads
9512K73 (2) 10mm ball stud 5/16-18 threaded

The idea will be to drill and tap two 5/16-18 holes. One in the base casting and the other in the Z axis bracket/nut. Once it is mounted I'll post pictures for that part of the project.

Regarding the Z axis lash, I had a thought: I think I'll cut the Z "nut" horizontally and add a couple screws to space it away from the other half. That would serve the function of putting a bit of preload on the nut/screw assembly. I'll follow-up with details when/if I do this.

Monday, January 23, 2006

Oil Analysis for My Truck

Before my extended warranty ran out I figured I'd get an oil analysis done to uncover any hidden problems. I bought a kit at a local auto parts store and, to my surprise, the analysis is actually done at a local company! Check out oil-lab.com for more details.

I received the analysis back only a few days after mailing it in and, low and behold, there was antifreeze in the oil. I wasn't entirely surprised as these engines are known to have lower intake manifold gasket leaks.

The part that surprised me was the willingness of the warranty company to fix the problem. I've heard horror stories about extended warranty places not wanting to fix anything unless there is a catastrophic failure of some kind. This was not the case! They were more than willing to fix the problem and actually complimented me on my proactive oil analysis!

To make a long story short, I took it to the local dealership and let them do the work. Should there be any problems I know they will take care of it long after the short-term extended warranty has expired.

I already have another analysis kit ready to do a follow-up check in a couple thousand miles. I'm hoping that truly solved the problem as I can't imagine what else could be leaking!!