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| The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20) |
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| awemawson:
I've been going crazy for two days trying to resolve an issue with being able to make this adaptor. The counterbored holes that the cap screws go in to mount it on the lathe spindle clash with the threaded holes that the collet chuck is retained by if both rings of holes are radially aligned '12'oclock to 12'oclock'. But in this orientation drilling holes to join the two sets of hydraulic oilways is dead easy. If I rotate the A2-5 mounting arrangement to clear the A2-6 cap screws then there is no way to drill the joining oilway as one of the mounting holes is in the way. But I had a flash of inspiration in the early hours this morning. The A2-5 collet chuck uses only 6 of the 12 possible mounting holes, and although the original chuck is mounted by 6 M12 cap screws arranged in three pairs there is no need for me to use this pattern as the spindle nose of the lathe is drilled and tapped for all 12 positions at 30 degree intervals. By much faffing about, rotating drawings and standing on my head I have (I think) at long last come up with a possible solution, that is each ring of mounting holes having 6 evenly distributed members but the A2-5 ring complete with driver peg hole is rotated 45 degrees counter clockwise relative to the A2-6 ring. It's not ideal as the holes that I will have to drill and plug that join the oil ways in the A2-6 spindle nose to the ones in the A2-5 collet chuck mount are at an odd angle and rather long at 89 mm (6 mm diameter) I now need to lie down in a dark room with a wet cloth on my head ! |
| nrml:
Perhaps doing those holes on your EDM would be more accurate than drilling them. Starting those holes at that angle on round stock and keeping them from wandering for that length would be a challenge with a 6mm bit I would imagine. |
| awemawson:
Well I'll certainly mill flats before centre drilling then peck drilling - even long series drills flutes aren't quite long enough, so swarf clearing is a must ! A few test drillings first I think ! |
| awemawson:
Having got totally confused with the relative location of the mounting and hydraulic holes on this adaptor I made up a 'prompt disk' with prints of the A2-6 on one side and the A2-5 on the other, and it rapidly resolved my dilemma. The problem was that I have drawings of the A2-6 spindle nose and recess but only the recess for the A2-5 part, and on some it is not at all clear from which side they are viewed. This of course confuses the rotational positioning of the oil ways as the other holes are symmetrically placed. Next issue was an oddity in Featurecam. You can define either a 'Boss' or a 'Pocket' from diameter and depth and you can give the side a 'draft angle' - I need this draft angle to be 7 degrees 7 minutes and 30 seconds - the program takes decimal fractions of degrees, so in this case 7.125 degrees which I duly inserted. Problem is, if you return to the pocket dimensions later for editing you find that it has truncated this to 7.1 degrees. The only place in the settings where you can set the precision of variables is set to XXX.XXX and changing it makes not a jot of difference :bang: However I discovered that there is a second way of defining the wall of a boss or pocket, that is by having a line on the drawing passing through X=0, Y=0 and at the desired angle to the Y axis, and this method SEEMS to give the desired precision, however the code it generates is MASSIVE ! Just the A2-5 boss on the adaptor generated 770 lines of code! Anyway I wanted to test if indeed the precision was adequate before committing, and dug out a bar end of 102 mm EN8 round to use as a trial cut. All set up and program loaded to the controller it started off very well, until there was an almighty BANG, the expensive 22 mm cobalt roughing cutter shattered and the enormous power of the X axis drive carried on pressing the broken cutter mangling the work :bugeye: It had cracked the CAT40 holder and mangled the BE180 collet . Stupidly I had accepted all the default values of speeds and feeds without checking them, and this was the result. Carefully looking at the damage to the stock I concluded that all the damage was above the finished surfaces, so if re-centred I could possibly continue if I could find another roughing cutter (it defaults to using a roughing tool followed by a finishing tool). Well I couldn't find one, so mounted up a 22 mm cobalt end mill, very conservatively changed the feed rates and started it off. The was 14:30 yesterday - it finished cutting at 20:30 last night - 6 hours of cutting - I don't think the Partsmaster has done such a long run EVER ! Got fed up watching it so rigged a camera to watch from the house! The way it is forming the taper is to orbit the part adjusting radius and depth in minuscule nibbles to closely approximate the angled line that I defined as the draft, and of course this gets rather tedious! The result is surprisingly good - surface finish not as good as a turned or ground finish obviously but it seems to fit OK. I tried measuring the resulting angle with my vernier protractor but to get anything like the angle is extremely difficult on such a short length. Bluing it the contact doesn't look too bad. I must say though, this is not the way I will be producing the tapers on the final adaptor - I will rough the blank out leaving the A2-6 'pocket' and the A2-5 'boss' parallel sided, and turn them on the lathe hopefully getting a far better finish and fit - this was just a test but even when turning I need to define the angles so probably will have to use the swept line method anyway. Still to decide how to fixture the part - the A2-6 mounting holes go all the way through so probably I'll mill that side first and use these holes before flipping the stock for the A2-5 machining. |
| awemawson:
An exciting day today :ddb: Firstly my son was able to deliver my haul of Soft Jaws won sight unseen on eBay all the way from Chippenham. Exciting for two reasons - due to Covid this is the first time we've been together for over a year, and secondly as there were far more in the box than I had thought - turns out that they are stacked two deep :clap: Haven't had time to give them a proper inspection but I think a 'good haul'. Secondly after he had left I was able to put the crane to it's intended use and remove the chuck to use it's female taper for making my male gauge in the next few days. It went largely uneventfully. Initially slackening the 6 massive retaining bolts, then when finger tight and the crane connected I applied a bit of lift and fully loosened the bolts. Initially there was an ominous creaking, and I realised that I hadn't withdrawn the spindle reducing sleeve that stops bars whipping in the tube. Quickly knocking it out with a bar through the chuck all was well, the chuck came away nicely, and although blooming heavy to manoeuvre it was successfully pivoted to clear the lathe enclosure and lowered onto my pump up trolley. No excuse now not to make that taper gauge ! |
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