08-04-2016, 12:59 AM
Hello All,
So the photos I promised from last time,
First I quick shot of My toolpost and "offsetting slide", the large knob on the top left hand side of the QCTP is the offsetting handwheel, it drives through a worm and wheel arrangement to turn a short leadscrew the moves the toolpost along a very short dovetail slide, this gives about 10mm or approximately 3/8" of travel, it's pretty hard going too but it allows for most thread cutting without need of a compound slide,
When it came to measuring the pitch between the two locating grooves, I used the two dowel method described above, it's a version of measuring a thread via wires,
Given that the Mascot is my go to machine for heavy roughing and general abuse my holders need to be made of something decent so I went straight to a piece of 2" square EN24 Alloy steel, It's hard enough as supplied and can be further hardened as required, it's not nice to cutting tools, but is absolutely machinable, so the right stuff for this job, especially as I had a leftover piece from a Job I had recently done. I'm not going to show bandsaw shots as I'm sure you've all spent enough time looking at a saw cutting through a chunk of steel, I cut the steel into a little pile of blanks all 125mm long except the last one as the off cut would have been useless I decided to make an over length holder for some as yet unknown purpose, but when I need it, well, I'll show it off then, It's as good a time as any to mention that the original holders were higher than mine, at about 2.5" high, they didn't need to be and I did some measuring to ensure adequate clamping etc, before finally going with a 50mm height.
The next step was to block them all down to a nice accurate 50mm square , (once again boring so no pics)
I took four blocks and lined them up neatly in my milling vise, as it was nicely trammed and I have power feeds on all axes on my Mill, I decide to use the cross feed rather than the long feed for most of the job,
As a result I could leave the vise in it's standard orientation, this made the accuracy of the distances between the vees easier to obtain as I have an "Anti climb" control on my long axis which removes all backlash from the long feed screw, which allows for climb milling normally but also means the the dial on the handwheel reads true regardless of which direction it was last turned.
So I got about the process of roughing and finishing the deep groove in the centre, leaving the Tee-slot "wings" till last, the groove is also toleranced but not as tightly as the position of the Vees so I did the deep central groove first, so that I could find it's centre when setting up for cutting the Vees, I centered on the slot after swinging the vertical head to 45 degrees, and by using the tilted tool to cut the champhers on edges of the groove, I easily found it's centre. By setting up this way you can acheive 141% accuracy as the angled cut is that much wider than a square cut would be, this means by use of a keen eye and a good steel rule you can achieve very much tighter tolerances than you might expect.
Finally it's just a matter of moving the table 50mm one way and then back by 100mm to get the correct spacing for the vee grooves, I cut the grooves all but 0.3mm to depth before rechecking centrality and finishing both groves with a fresh endmill,
I'll get back to work now and give a little bit more in a few days as time allows.
Best regards
Rick
So the photos I promised from last time,
First I quick shot of My toolpost and "offsetting slide", the large knob on the top left hand side of the QCTP is the offsetting handwheel, it drives through a worm and wheel arrangement to turn a short leadscrew the moves the toolpost along a very short dovetail slide, this gives about 10mm or approximately 3/8" of travel, it's pretty hard going too but it allows for most thread cutting without need of a compound slide,
Given that the Mascot is my go to machine for heavy roughing and general abuse my holders need to be made of something decent so I went straight to a piece of 2" square EN24 Alloy steel, It's hard enough as supplied and can be further hardened as required, it's not nice to cutting tools, but is absolutely machinable, so the right stuff for this job, especially as I had a leftover piece from a Job I had recently done. I'm not going to show bandsaw shots as I'm sure you've all spent enough time looking at a saw cutting through a chunk of steel, I cut the steel into a little pile of blanks all 125mm long except the last one as the off cut would have been useless I decided to make an over length holder for some as yet unknown purpose, but when I need it, well, I'll show it off then, It's as good a time as any to mention that the original holders were higher than mine, at about 2.5" high, they didn't need to be and I did some measuring to ensure adequate clamping etc, before finally going with a 50mm height.
The next step was to block them all down to a nice accurate 50mm square , (once again boring so no pics)
I took four blocks and lined them up neatly in my milling vise, as it was nicely trammed and I have power feeds on all axes on my Mill, I decide to use the cross feed rather than the long feed for most of the job,
As a result I could leave the vise in it's standard orientation, this made the accuracy of the distances between the vees easier to obtain as I have an "Anti climb" control on my long axis which removes all backlash from the long feed screw, which allows for climb milling normally but also means the the dial on the handwheel reads true regardless of which direction it was last turned.
So I got about the process of roughing and finishing the deep groove in the centre, leaving the Tee-slot "wings" till last, the groove is also toleranced but not as tightly as the position of the Vees so I did the deep central groove first, so that I could find it's centre when setting up for cutting the Vees, I centered on the slot after swinging the vertical head to 45 degrees, and by using the tilted tool to cut the champhers on edges of the groove, I easily found it's centre. By setting up this way you can acheive 141% accuracy as the angled cut is that much wider than a square cut would be, this means by use of a keen eye and a good steel rule you can achieve very much tighter tolerances than you might expect.
Finally it's just a matter of moving the table 50mm one way and then back by 100mm to get the correct spacing for the vee grooves, I cut the grooves all but 0.3mm to depth before rechecking centrality and finishing both groves with a fresh endmill,
I'll get back to work now and give a little bit more in a few days as time allows.
Best regards
Rick
Whatever it is, do it today, Tomorrow may not be an option and regret outlasts fatigue.