Wednesday, March 5, 2008

Files - The tool

Using a File

I want to start this week’s recap talking about the importance and the power of the file. As an engineer, I have always heard stories from older machinist about how they started out with a file, as part of their apprenticeship. “You first master the file then move on to machines,” they often say. I am very thankful for this simple and sometimes ignored instrument; the proper use of it has allowed this project to move forward. I was never an apprentice; as an engineering student they don’t teach you much about machining, they teach you what they are for but most of my instruction was practical working with supplier shops or the occasional machining by my self after breaking into MIT’s machine shop and hotwiring the machines. So I missed out on the filling thing and as I started to research this project I came across scraping, the technique used to make very precise machines. The best machines in the world are made by scraping. I did not consider it as a possible technique to use because it’s considered complicated and time intensive. But filing is close enough and we have had to resort to filing to accomplish the proper flatness to mount our rails.

See, this week we found ourselves in a bind. The two techniques that we had in hand for mounting the rails on flats failed. For one we did not have enough “plastic metal” resin for our application. It was not easy to procure in Medellin and the last two cans that I ordered from the states had arrived cracked and spilled. Also the error on the steel tubes and the warping after welding had limited our ability to adjust the rails with shims. Also trying any kind of grinding off the machine was impractical and on the machine itself there where problems with guaranteeing straightness.

However with the use of a precision bubble level and a straight edge (common machine shop tools) we managed to file the mounting surfaces flat and straight within the sensitivity of our level which was of 50 microns per meter. I know to some it may seam intimidating to use hand filing but with great care and patience the results are really good. It took us a whole day to file both rail surface, we started out with hand grinders and then moved on to hand filing. I was personally amazed with the results achieved with a $5 file. The most tedious part is checking the progress; it really helps to have a second person for this. Not only are there two sets of eyes evaluating, but it also helps to take turns and keep you company. I noticed it was important not to file too hard; for one, it did not come out as good and the more tired you get the more sloppy you become so doing with two people is a great plus.

Wednesday 27th

Aligning the rails has failed. After the long night on Tuesday I sent the group home by 8 to catch up on rest. Lina and Camilo completed their research on the large casting for the Z-axis; they talked with the university professor, visited suppliers, mold makers and prepped to start making the mold them selves. Professional mold makers (for the metal casting industries) where charging upwards of 400 dollars US for the mold plus they where going to take over a week. Since we did not have the time we decided to do it our selves.
We got a number of pieces for X-axis delivered from the plasma cutter and this allowed us to spend some time on Wednesday and Thursday tacking and welding this axis together. The missing pieces should be done by Monday and the final welding will take place early next week.

I also got a glimpse at the software and electronics. This part may prove to be the most intimidating to people building their own machine and its one that has started to worry me since the cost are starting to grow. The enclosure for the electronics itself is expensive and it has a number of components including cables, cable carries, terminals, connectors, limit switches, e-stop, fuses and more. I am also aware that I have not spent enough time supervising this group and what may end up happening is that people design the most modular and presentable solution, which may not necessarily be any better or the least expensive. So I plan to go in Monday and question what they are doing and cut costs everywhere I can.

Thursday 28th

At least the rest of the group got some rest. I was up late working on the upcoming logistics and financials of the project. We came in determined to flatten our mounting surfaces for the Y-axis. The night before we had bought the appropriate files and grinding disks. Esteban got started, and he was still going at it strong into the lunch hour. It was clear it was taking too long. And another run to the hardware store was needed, for a 9in grinder. The length of the disk would allow us to use the flat portion of the disk and speeding up the process without digging dangerously into the work piece. By 5 pm both sides where rough flattened. It was time to fine-tune them. For this all four of us were involved - Esteban, Juan and Pedro and my self. This way some of us were testing and marking while others filed away one side. On the other side we tested and measured the actual rail placement. With the appropriate pizza dinner we tooled into the night but we finished. As I mentioned at the beginning of this post, the files did wonders. I couldn’t be happier. The results were better than expected. Now we have hard surfaces that can continue to be fine-tuned through out the life of the machine. We left them at plus or minus 50 microns per meter flatness but this can be improved with actual scrapping and more time in the future.

Friday 29th

Friday was all about staying on schedule. We placed the holes for the second rail after building an alignment rig. This way we guarantee that both rails are in parallel. The model for the casting got plenty of attention. Getting the draft on the sidewalls is proving more challenging than expected. There is actually a bet in the model shop that the casting will not come out. They have never seen something this complicated and if it does work they promise to hang a picture of it in the shop’s wall.

The plan was to fishing the day with a concrete filling of the horizontal members so we had to flip the machine on its side, mix the concrete and stuff it in. We manage to do this in less than 2 hours so. By 7:30 we where cleaning the shop and putting the tools away. Progress is back on track, thanks to a file, and to some late nights. I am flying out to Boston again on Saturday and back on Monday. I will be bringing back the pulleys for the spindle drive and a few power supplies. It will be my last trip of this sort, after this it is the last two weeks stretch. And it will be a final stretch; the shop space at the university is due in two weeks.