February 16, 2011
Started on a Poppin flame licker engine. I'm making it 1.5 times scale, just to be different. After terrible results with the ebay bar, a neighbor gave me an old window weight. Same bad results - lots of inclusions and voids in the casting, and it ruined the HSS tool I was using. No big deal, but it will have to be reground.
So, off to McMaster-Carr to order stock. Price (including shipping) for 1" and 1.5" diameter bars (12" of each) was less than 30 bucks. Not bad considering how heavy it is, and the fact that it was in my hands the very next day without me having to leave the house. The new stuff machines very nicely, in contrast to the crap I had been trying. It's slightly oversized (1.5" bar is actually 1.58"), so plenty of room to clean up and still hit the numbers.
Put that on hold to try to complete the Jingle Bell engine I saw here. I'll have to go back to it while I wait for mill parts to arrive.
January 4, 2009
February 16, 2011
Earlier this month I was cutting some nasty cast iron bar I bought off ebay. (Note to others: spend the money and get decent cast iron from a supplier. The cast window weights are full of crap, have a terrible surface, and generally will waste more time and effort than they are worth.) I was smart enough to grind the outside on my bench grinder to remove the majority of the hard scale, but even so it gave the little machine a pounding. This loosened up things quite a bit, to the point I was having problems getting a good finish. The whole carriage was visibly rocking at this point.
So, time to readjust the carriage. It has been a while since I cleaned it up, too. Off it came. Where upon I discovered that two of the six screws had backed almost completely out! I disassembled the apron, and cleaned the recesses for the leadscrews on both the crossfeed and the compound. I carefully cleaned and re-lubed eveything, then proceeded to reassemble. Adjustment was a little easier - although still a pain in the butt - than the first time, because I understand better how the forces act on the parts, and how much play I need to take out. I also have developed a better 'feel' for how tight the carriage and slides should be. The cross slide and compound gibs have bedded in quite nicely at this point.
While I had everything apart, I decided to measure the ways and check for wear. To my pleasant surprise, there was none that I could measure, and no noticable wear marks in the ways or leadscrew. This was, to me, surprising, as I initially had the lathe tightened up far too much, and I have never babied it. Over time, I have learned better how tight it really needs to be, but it was good to know my inexperience hadn't ruined things.
Those of you with a minilathe understand just how fiddly it is to get the carriage adjusted correctly. With help from minilathe.com and some other sites, I did get it done, but there are complications. Aren't there always? In order to get the correct adjustment, the outside screws need to be barely finget tight. Naturally, this won't hold up very well (any vibration loosens them), and a fix needed to be found. Loctite is usually the answer, but in this case, since the screws weren't tightened down, it didn't want to cure. Red loctite will usually hold under these conditions, but I didn't want to permanently fix the screws and make future adjustments impossible.
My solution was to use the old nylon string trick. Any cheap nylon string trimmer line will work, and it's cheap as well. You drill through the screws at a right angle to the threads, about .080 from the end of the screw. Size the drill to just a hair under the size of the nylon string you've got. Force a length of line into the hole through both sides of the screw. Then, using a sharp utility knife, trim off the nylon to be flush with the outside diameter of the threads. When you start the screw, it will be pretty tight, but a couple of turns will cut the thread into the nylon. It holds just enough to prevent backing out from vibration, but allows easy adjustment.
Hope this helps.