Build Thread- BP series 1 threadmaking

[bartL]

Hello,

Is there someone on this forum who is using a series 1 for thread making? I would really like to rebuild mine so it will be able to do this. I'm especially interested in what's the best way to measure the exact spindle speed and how you will switch your turning direction that quick.

Best regards,
Bart

[jmelson]

Originally Posted by bartL Hello, Is there someone on this forum who is using a series 1 for thread making? I would really like to rebuild mine so it will be able to do this. I'm especially interested in what's the best way to measure the exact spindle speed and how you will switch your turning direction that quick. Best regards, Bart

I assume you are wanting to do rigid tapping when you say thread making.
If your machine doesn't have a spindle encoder, it is not possible to do this without major modifications. Generally, you are not going to be able to add this feature to an existing controller.

Depending on what Bridgeport milling head you have, this could be anywhere between difficult and impossible. The problem is the way most Bridgeport heads were built, there is no access to the spindle so that you can add on an encoder with a little timing belt. So, that't the first hurdle, and I have no solution. The only scheme I think that has any hope of working is to drill holes in the side of the back gear housing and put a pair of gear tooth sensors in to pick up the teeth of the bull gear. I have done this with one sensor to make a spindle tach, but you need two sensors with a precise offset between them to get a quadrature signal. Then, you need a 3rd sensor to pick up a magnet or vane to make the index pulse.

Then, you need a CNC program that can handle spindle threading. Most of the hobby-level programs do a pretty poor job of it, if at all. EMC2 does, however do real spindle threading, accurately keeping the Z axis in sync with the spindle rotation. Due to the Bridgeport head issues mentioned above, I haven't done it on that machine, but have put a spindle encoder on a Chinese mini-mill where the encoder mounting was trivial. It does an amazingly good job on that machine.

I have used a Procunier "CNC" tapping head on my Bridgeport with good results. That is a model 15000. It has no overload clutch, just a clutch that reverses its own spindle at 2X main spindle RPM when you pull back on the tap. So, you calculate the feed needed to tap at the desired RPM, feed in to required depth, then retract at 2X that feed. If the feed is a hair slower than required, the tap gets ahead and then the clutch slips a little so everything stays in sync.
This works amazingly well. The only problem is this tapping head is so long that it barely fits to do work held in the vise, and wanders a bit. I like to use these combined drill-taps that spot, drill through and tap in one operation. So, now I do that on the mini-mill due to the better setup. Someday I may figure out how to fit or adapt an encoder to the Bridgeport.

Jon

[5S Dude]

We use a Tapmatic RX50 Self-Reversing Tapping Attachment with a “Tommy-Bar” on our manual Bridgeport with great success from #6 through ½-13

I’m currently using a Procunier 57410 Tension Tap Holder on our V2XT and we’re tapping ¼-28 blind holes .215 deep using the following code.

;1000(TAP 1/4-28)
N1 T1 M6 ;(3/16 END MILL)
S3750 M3
G00 X.8961 Y-1.38
Z.1 M8
G1 Z-.125 F5.0
G01 F10.
G03 Y-1.3688 I.8961 J-1.3744
Y-1.3913 I.8961 J-1.38
Y-1.3688 I.8961 J-1.38
Y-1.38 I.8961 J-1.3744
G00 X.8961 Y-1.38
G1 Z-.22 F5.0
G01 F10.
G03 Y-1.3688 I.8961 J-1.3744
Y-1.3913 I.8961 J-1.38
Y-1.3688 I.8961 J-1.38
Y-1.38 I.8961 J-1.3744
G0 Z.1
M20

N2 T1 M6 ;(1/4-28 TAP)
S750 M3
G00 X.8961 Y-1.38
Z.1 M8
G84 X.8961 Y-1.38 Z.19 F26.78
G80
G0 Z.1 M9
M22

I would like to try my hand at Thread Milling this with a .180Ø Carbide Thread-Mill using the G13 command if any of you have programming examples you can post.

[bartL]

Jon,
Thanks for your clear explanation. I've never investigate if it's possible to assemble an encoder somewhere on the head. I assumed this shouldn't be the problem but it seems it can be a serious problem.
My biggest concern was to change the turning direction of the spindle, I always have to do it by hand but you'll only use it to choose turning direction before milling not during work.

5S dude,
Thanks for the information. The problem is that it's very hard to get the right tooling for my BP because of the QC30 holder. And when I finally found something it always has English (inch) measurements. We are only used to work with metric measurements.

Best regards,
Bart