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| Another new project... a QCTP (Quick Change Toolpost) |
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| AdeV:
--- Quote from: madjackghengis on September 05, 2010, 09:05:17 AM ---Hi Ade, I keep a starret level on my mill table, it has two bubbles at right angles, and is pretty accurate matching up bubbles pretty close with my machine level, and I often use a level to get a piece in the vise close enough for regular kind of work, like putting a handle on a tool post. --- End quote --- Another cool idea, I like it :clap: It wouldn't work on my mill, unfortunately, as mine's at least 1/2 a bubble off level... Looks like I'll be shimming it some time soon... --- Quote ---As to dimensions of a large tool block, I suggest you find one you feel is the right size, lay a couple of dowel pins in the female dovetail, use an appropriate sized adjustable parallel to tighten up the dowel pins (they need to be about two thirds the depth of the dovetail slot for accuracy), and measure off the parallel, and use the same pins and parallel when you make your slots. I'd suggest making a "master slot" blank, and use it for testing all your future tool holders, to keep from creeping larger or smaller, incrementally. --- End quote --- It's the finding one that's the issue... Anyway, I've given up trying to match an existing one, and am going with my own dovetail size (2" root x 0.5" depth), In fact, I'm about to go out & cut the first one... |
| AdeV:
Tonight's write up will be a little brief, as it's late o'clock, I'm starving hungry, and swarf isn't edible unfortunately. :doh: Today, I worked some more on the main body. First job was to cut one of the long sides down to the top of the dovetail: 18mm roughing cutter, pushing it until it produced nasty burny blue chips. Then, since the mill wasn't complaining, I carried on. I only got burnt once worth a mention... Once the holder was milled to exactly 4.010".... erm, OK, approx 4", I turned it 90o in the vice, and used the edge finder to locate a corner. Next job, rough cut away the material either side of the dovetail: Same cutter, same colour chips. Lots of smoke. Mmmmm, smoke. The shallow groove was a reference cut to make sure the dovetail is the right width, and that I'm cutting in the right place. I was.... so the non-dovetail portion was taken down another 0.500". Then, load my newfangled 1.25" dovetail cutter (a snip at £20 from Chronos - hardly worth keeping sharp at that price), and get cutting. This is a miserable operation on my mill; I've got some wear in the dog clutch in the top, so it clatters like a bugger at slow RPMs, unless I use my fingers to keep a bit of resistance on the quill. I think what's happening is, as a flute clears a chip, the cutter sort of springs round, until the next flute engaged which slows it down, then the dog clutch catches up with a BANG; repeat 200 times per minute and it gets quite boring quite quickly... Yet another "must fix it" job... ANYWAY, I did manage to take one photo; this is the second to last cut & is much easier on the cutter than the previous cuts, hence having a spare hand to run the camera: Once the dovetails were cut to size, I used a deburring tool to mill a small 45o chamfer on the top edge, then a brief whizz round with the file just to deburr & soften the edges slightly. Last job tonight, I don't bl**dy believe it, YET MORE SLOTTING! Using the 1/4" cutter (as I happen to have a 1/4" radiusing tool which will radius the pistons just right). The cutter moaned if I tried to take anything more than 0.100" at any more than a glacial feed rate. This got old very quickly, so I slapped in a 6mm roughing cutter & chopped the piece out in one fell swoop. Yeah, it smoked at me, but it got the job done. Then, back in with the 1/4" mill to tidy up the edges. A bit more faffing with the file, and here's the result: Starting to actually look like something now.... I have a lot of machine marks to clean up. Not looking forward to that job... Tomorrow, I will try to finish the other dovetail, then I just have a bit of work to do on the underside of the body and I can move on to some other parts... Question: I've made the cam out of 303 stainless steel: What material would you, gentle reader, recommend for the pistons? I'm wondering if it's worth avoiding S/S to avoid galling, and I'm thinking maybe brass or phospher bronze might be an option? |
| madjackghengis:
Hi Ade, were I me, which I am, I'd use a piece of aluminum bronze if I had one laying around, stainless does gall easily, particularly 303, and the aluminum bronze is about as hard a bronze as you get, and would probably give the best bearing surface for the eccentric. It's probably going to be turned a few dozen times at least, I'd say. Worth taking account for some friction. I expect once you've got a few tool holders, you'll be as well off as if you bought them, and from then on, all the ones you make, will be as if you'd bought the original post, so you didn't lose much of anything in not finding dimensions. I looked through my catalogs, and books, and didn't find any reference with dimensions of the dovetail in any of them. As long as it's big enough, it'll get you through the day. I think that spline issue would about drive me crazy, my tractor was doing that a few years ago, ended up having to make a new clutch for the PTO so it'd stay engaged and cut. One of these days I'm going to buy a few roughing cutters, I keep reading about people using them, and they sound like a good piece of gear. Looking good so far :beer: :bugeye: mad jack |
| AdeV:
--- Quote from: madjackghengis on September 06, 2010, 07:52:36 AM ---Hi Ade, were I me, which I am, I'd use a piece of aluminum bronze if I had one laying around, stainless does gall easily, particularly 303, and the aluminum bronze is about as hard a bronze as you get, and would probably give the best bearing surface for the eccentric. It's probably going to be turned a few dozen times at least, I'd say. Worth taking account for some friction. --- End quote --- Well, I didn't have any lying about (I only have a lump of brass, but that's earmarked for a different project), luckily my metal merchant had some kicking around. It's not cheap though - £40+vat for a 4" length of 2.25" bar! Still, that gives me loads to make the pistons with, & some left over for future projects. As for the pistons, the more I look at it, the less I like the rectangular shape, I think I'd prefer a squarer piston, to give better side-to-side support. I also need to figure out how to make the pistons stay inside the unit; I'm thinking a small flange on the back, and an appropriately recessed area inside the bore (I have to cut a recess, otherwise I'd never get the cam sleeve in... --- Quote ---I expect once you've got a few tool holders, you'll be as well off as if you bought them, and from then on, all the ones you make, will be as if you'd bought the original post, so you didn't lose much of anything in not finding dimensions. I looked through my catalogs, and books, and didn't find any reference with dimensions of the dovetail in any of them. As long as it's big enough, it'll get you through the day. --- End quote --- I think you're right; I still need to make the holders; not sure if I just bite the bullet & buy some steel to make a stack of them, or whether to make 1 from ali first... choices choices... I'd better finish the main toolpost first, lots to do on that yet. --- Quote ---I think that spline issue would about drive me crazy, my tractor was doing that a few years ago, ended up having to make a new clutch for the PTO so it'd stay engaged and cut. One of these days I'm going to buy a few roughing cutters, I keep reading about people using them, and they sound like a good piece of gear. Looking good so far :beer: :bugeye: mad jack --- End quote --- You're right, the clattering just sounds so wrong, so bad, that I really ought to do something about it. I can usually avoid it by setting my cuts up carefully, and by equally careful speed/feed rates. If I keep the cut aggressive, it tends not to clatter... I can highly recommend the roughing cutters, they're great for rapid removal. The surface finish from the side of the cutter is dreadful, but then it IS a roughing cutter. The end cut can be pretty smooth, certainly little worse than my best endmills. |
| AdeV:
I've not abandoned this project... but it took 2 days to cut the 2nd dovetail: Day 1 to bulk-remove material to dimension, Day 2 to rough the dovetails, cut them properly, then cut the hole for the piston. There's no action shots, because they look the same as before. When roughing the material off, I had to stop every 0.200" to let the block cool from "FMTH" to merely toasty... So, here's the result: As you can see, I've gone for the bigger square piston rather than the tall thin one. I obviously still need to open out the original hole, I ran out of time tonight. I've also had a little go at draw filing on the first dovetail, hence the slightly odd appearance of the marks. A bit more time & it should look loverly. Finally tonight, a little light relief..... How does one transfer oil from the big can to the little can, without spilling any, when you've not got a handy assistant to hold the funnel? Answer tomorrow... |
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