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| Miner:
Wong, Everybodys methods and favorite techniques are a bit different. When it needs it, I make a layout as a general check for miscounting handwheel turns. But if your leadscrews are in pretty good shape and dependable for measurement? I don't use any center punch marks at all. Locating your marks and starting the hole with a center drill by coordinate measurement works real well. It does take a bit of time and practice to get fully used to using that system though. That's where those edge finders come in. If it was good enough system to use for the super accurate Moore jig borers and grinders? Then it's more than good enough for me. Having dial indicators for measureing the slide movements, Or a DRO makes the job that much easier. It is a bit slower way to work since your using a center drill to start, Then switching over to your drill. But if you factor in the fairly accurate center punching time, This method could be a bit quicker. If my memory is correct, It's called the Cartesian coordinate system? But the correct name is not that important. It's the technique that is. Pete |
| Fergus OMore:
Yes, it's the cumulative Descartes stuff which many of us use. It is far less prone to making mistakes with 'Simple Arithmetic' going from making what is in effect establishing a zero at each centre drilling. Of course the zero, may not be accurately determined. Someone mentioned 'Tubal Cain'- not this Johnny Come Lately but the Tom Walshaw variety and he set off to knock the so called experts who were all called to centre on two scribed lines- and none of them could. Interesting stuff. And it all gets worse with worn leadscrews 'et al' :smart: |
| wongster:
Thanks all for your input. I'll go it without centre punch for the next piece and use a corner as reference. Using the centre hole location is convenient the drawings uses that as the reference. I read from one book (can't recall the name) that if the drawings uses a certain point as the datum, all measurements are relative to that datum. Using a corner of the workpiece is more convenient for me as I'm more familiar with it. Regards, Wong |
| wongster:
The Base I started off my Sunday morning redoing the dimensions of the Base of the Set-Over Centre using the bottom right corner of the workpiece as datum (hope I'm not using the wrong word here). The drawings from Hemingway have the location of all features relative to the centre 5/16" BSF tap hole, which I followed when fabricating the Slide. Counting the number of turns on the dial is easier with the datum from the bottom right corner and I was moving the table in one direction, thus not having to worry too much about backlash. The stock was cut almost to length on the bandsaw and trimmed to 3" as called out in the plan. This is the 2nd time I'm hitting the exact dimension - a real boost of confident. Wishing for more as I progress... Redoing the drawings with the bottom right corner of the workpiece as datum. The stock was held in the vise and carefully tapped down to ensure full contact on the parallels beneath. The layout lines can be seen in the pic. No punch mark this time as advised in the forum. Measuring the tip of the Proxxon Edge Finder. It actually measures 0.2", kind of strange from Proxxon which has everything else in metric. Finding the edge in Y axis. The table was moved over by half of the tip of the Edge Finder to zero the spindle axis to the edge of the workpiece. X was next. Centre drilling of the 5 holes for later operations. This is the first time I centre drill all the holes before drilling. I always like to centre drill and drill through each hole before moving to the next location to reduce the number of times I have to move the table (and save on counting...). Drilling the holes using 1/4" drill. A pair of machinist clamp was deployed as limits for the slot to be milled. There are 2 slots in this part; one connecting the 2 holes on the right and the other, the last 2 holes on the left. This will save me from having to count the number of turns I've made to focus on the job at hand. I plan to make mill stops in the near future for all 3 axes to ease the process. Begin milling the slot with a 1/4" slot drill. I started with depth of 0.2mm per pass but went on to 0.5mm. Slot done. The 3/8" slot 1/4" deep was next. A piece of scrap used as depth stop for the Z axis. Wanted to use machinist clamp for this but I couldn't locate the other 2 pieces I bought. Done! Time to test if the cap screw will fit. Unfortunately not... The supplied 1/4" BSF cap screw's head measures slightly larger than 3/8" and the 3/8" slot drill from Sherline cut the slot at 0.372". The 0.372" seems to be consistent with the slot I did in the Slide before widening. I will be buying another one locally for further testing. Till the next session, be blessed. |
| andyf:
[quote)... The supplied 1/4" BSF cap screw's head measures slightly larger than 3/8" and the 3/8" slot drill from Sherline cut the slot at 0.372". The 0.372" seems to be consistent with the slot I did in the Slide before widening. I will be buying another one locally for further testing. [/quote] Hi Wong Turning the head of the screw down by a few thousandths would be easier than widening the slot. Andy |
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