That new draw bar will be a nice touch
I'm going to get going on my new thread to convert and modify my Quality Machine Tools PM-25-MV mill. For those that don't recognize it it's a variation on the BF-20 theme marketed by the QMT guys.
The 25 has about a 1HP motor per the spec but otherwise shares the same travels as the 20. I had some initial difficulty in getting it back together after dragging it to the basement. Got that sorted out and then the motor controller died on me. After some mail parts swapping they paid to ship the head back and repaired it there. It should be on its way back this week.
In the mean time I have put the X2 to work to make my first mod parts. I made some tram tunning blocks like machinechick showed off to allow me to fine tune the X tram using set screws instead of tapping with a hammer back and forth. If I need to tilt the head on an angle I can loosen one and swing it out of the way. Will need to drill and tap a 1/4"-20 hole in the carriage on both sides for them.
Second was a way to mount an X scale using the existing table stop nuts on the front of the table. I measured out the scale and I think the clamps will allow me to get the scale mounted with enough clearance to attach the readout to the saddle and still clear the gib lock handles. I wanted to have it tilted upwards on the mount but that doesn't appear to be possible really given the clearances. If these work then no modifications or holes will be needed to get the X scale mounted. Next will be the Z axis since I want to avoid using the quill for Z movement whenever possible. Last will be the Y but that may not really happen if I CNC first.
CNC conversion is now a priority. It appears I am developing carpal-tunnel from my day job and cranking on handles at night is not helping at all. I may be a one-armed man for a few months here in the future and so I am scrapping my plans of home-built circuitry and I'm going to look at getting some commercial drivers and so-forth. I'm going to see how well my existing 425oz/in Hobby-CNCs can move the tables around. I'm thinking something with more beef is going to be needed on the Z though.
First pic is the PM-25 in front of the X2 for a comparison.
Next shot is the X2 face-milling the material for the scale clamps with a Glacern FM-45 2.5" face mill.
Next shot is the two pieces ready to be drilled for the clamp screws.
Last shot is the X tram tuners on the left, one scale clamp on the top left, and the stock for another clamp and base on the right.
My tapping on the first part went poorly. Broke the 6-32 tap in the first hole. I've just got some ACE hardware Irwin taps on hand but I'm going to be going to HSS spiral taps in the future. instead of scrapping the toasted part I used it to make the top clamp by cutting off the section with the tap lodged in it. I've been using the spindle on the X2 to tap by putting it in nuetral and turning the tap using the spindle drawbar.
I'm waiting on a metric drill and endmill to drill the clearance hole and counter bore for the M6 socket cap that attaches the base to the front of the table. Using the existing hardware means metric sizes. The 11mm end mill will be used to cut a counter bore to allow the socket cap screw to fit flush under the scale.
Once all that is done I'll make the final cuts to the base to remove the corners outside the width of the top clamp. I imagine I will also need to fabricate some type of chip guard for the scale.
I'll try to keep this updated with successes and failures as I go.
That new draw bar will be a nice touch
One X DRO clamp down. One to go. Then I need to design an attachment for the scale face to the saddle. I goofed up and didn't get a center-cutting end mill for the 11mm counterbore for the mill's stop bolt but the 7mm through hole was enough to allow the end mill to plunge in. I also used a 5/16" endmill to recess the clamp bolts a bit.
I clamped the scale on with just the one and let it butt against the gibb clamps just to enjoy the digital goodness of seeing the little display count off while I cranked. That's going to help. Eventually I need to change it to face up instead of forward. It's not real easy to read this way. But it will do for a while I think.
The clamps are done so now I need to work on the mount for the saddle to attach the scale electronic unit. I had not noticed the small ledge between the side of the X table and the front of the saddle. That's going to add some complication. I'll start drawing up the mount this week. I got raped on taxes this year so my Z scale will have to wait a bit.
I had to mill off a little of the electronics housing on the top. It would protrude above the top of the table even with the scale bottomed out on the gibb screws. I took off about 0.035" and that opened a good gap. I did notice that one of my gibb screws is bent. I guess I snagged it cranking the Y at some point and bent it. Anyone know a source to get a replacement? That forces the scale up a little high and I'd like enough room to put up some sort of chip cover for it over the top of the scale. I'd have enough space I think if the gibb screw wasn't wobbling around.
Downloaded and started using Google's Sketchup to work out the center mount. That little ledge at the bottom is tough to measure without tearing the Y axis handwheel off but I got a pretty good idea of the space back there from some gauges. I modeled the scale to make it easier to test fit it together.
The bad news is that I can't use the existing holes for the center pointer to mount the scales electronics. There is not enough clearance to flush mount the bolts and the scale face will cover one hole leaving me with only a single bolt to hold it. Seems like that could allow it to pivot and cause inaccurate readings. So it appears I will need to drill and tap two holes to the sides of the center line. I was hoping to avoid that but I don't see how with the scale's dimensions.
I think I have a workable center mount. Bottom bolts holes will have 0.060" of slotting to allow for the float in the table clamps. Rear attachments for 4-40 screws are also slotted to make the alignment less critical. Will be the most complicated thing I've made thus far LOL. I still pucker a bit slotting with the 'math-practice' wheels on the X2. Wish my mill head would get back in on the PM-25 because working in .100" turns is tons easier.
I'll pick up my stock material for this tomorrow. No scrap on hand with the right dimensions.
I just stopped by your thread following your link from the tapping questions.
The mill you are working on seems to be a fair sized machine and a good looking one too. I have a small SX3 CNC mill that is pretty good but the travels are lacking in the Y axis. What are your travels on this machine? If i remember correctly I have 12" X, 6"Y(is actually a little less in the Y) and 9" Z. I hope the DRO works out well for you.
It's a very similar mill to the G0704 mill in the threads here in benchtops. The travels are 19" X by 7" Y (6" Y if you have the rubber way cover and bellows Z cover installed.). The long table and increased Y was a big upgrade from my X2. The motor is 1KW (rated not sure about actual) which is another big upgrade. 3000RPM top speed. The table is great, not concave like my X2 and it's much less prone to vibration problems.
The motor controller issue was my only problem and that's looking like it's solved and the head should be heading back to me this week.
As an update:
Turns out those 4-40 tapped holes in the scale were actually M3. I was test fitting some screws at the hardware store and they were going in but just not feeling right. Lucky for me the little M3 button head screws they had JUST fit into the slot so no modification needed and now they fit properly and tighten nicely. I cut the thickness of the rear section about .010" thick to try and fit it as close to perfect as possible. After taking off 0.006" it seems to fit really close. Flat against the saddle, and just touching the back of the scale slider without pushing it forward any. Now I just need to pucker up and drill/tap the bolt holes for the center bracket and I'm done with the X axis.
I'm going to go have a nice cold drink. One modification done. The scale is fully mounted and working. I did flub up a bit drilling the holes. I somehow got off center as I clamped my guide in place and drilled the hole high. Not enough to ruin it but noticeable. That put my other center punch mark off and even making a new guide block bolted with the first tapped hole couldnt seem to keep the bit from being pulled into that punch mark. So the bolts are a little cocked but there's enough slot in the center bracket to deal with it. Makes me not want to do much more hand drilling though or I'm going to need something easier to see where the point is landing at least when I do the column.
I axed the cutout in the middle of the center bracket. Didn't want the old ruler pointer/center stop holes in the saddle to show through.
I just wanted to write you a quick note on how I hand drill. If I understand how you did it, there is a better, easier way. First off, don't use those silly "guides" that keep the drill straight, those might be ok (not really!) for tapping, so you don't cock the tap and snap it; you sure don't need it for drilling, just relax and have confidence, you can hold the drill at pretty close to a right angle if I can, those guides just block your view, slip, etc. (sorry if I misunderstood you on this point)
Here's how I do it, works everytime for me: 1) Use a plug in drill (non-rechargable), a good quality one with like an 6+ amp motor, so you have enough power!, 2) Just layout where you want the hole, use some dykem or a sharpie marker, scribe, etc. if your concerned about it being accurate 3) center punch where the hole is going to go 4) start the hole with a center drill or a combined center/countersink bit, just like you would when your starting a hole in any metal working (skippping this step will cause you 90% of problems in hand drilling) 5) then finally with small diameter holes like the screw holes for the scale , just drill the hole. For larger diameter holes just work you way up, drilling one bigger hole after another till your at the size you require.
Don't give up on hand drilling, it's easy, accurate enough, and will save you a lot of hassle, just give up on the guides!
I just wanted to add to machinechick's comment that if you check the hole location after the first step is drilled you can verify if it has wondered off location and if so take steps to work the hole back towards the correct center. If drilling through the material you can usually file the hole in the correct direction to correct it, but that is not so easy with a blind hole and you may have to angle the drill as you drill a small amount and re-check the location.
I think your DRO addition has turned out very well and it looks like a good compliment to your machine! I will be watching to see the continued work with your machine.