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TomS

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Finally got some shop time today and installed the repaired BoB. Fired up the mill and it now works as it should. M3 and M4 work as expected. Here's a short video showing the spindle rotating CW then reversing. Looks like I need to look at reducing the lag between the spindle reversing and the Z retracting.
 

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spumco

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How's the cycle coded? I'm just asking to see if the lag is in the code or in your VFD settings. I seem to remember you talking about a braking resistor - that should let you stop and reverse on a dime.

Good to hear you're up and running, by the way!
 

TomS

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How's the cycle coded? I'm just asking to see if the lag is in the code or in your VFD settings. I seem to remember you talking about a braking resistor - that should let you stop and reverse on a dime.

Good to hear you're up and running, by the way!
The gcode file is attached. I reduced the dwell from .5 second to .25. I can tighten up the accel and decel VFD settings and see how that works out. I haven't done any CNC power tapping so I'm being extra cautious. Don't want to break taps and ruin my only piece of material.

Edit: Yes, I have a braking resistor.
 

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Boswell

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I did not realize that it was possible to TAP using Mach3. The z-axis is tightly controlled but spindle speed, not so much. You don't have Acceleration control for instance on the Spindle speed. Looking forward to how this works out.
 

TomS

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I did not realize that it was possible to TAP using Mach3. The z-axis is tightly controlled but spindle speed, not so much. You don't have Acceleration control for instance on the Spindle speed. Looking forward to how this works out.
I guess I'm going to find out. The floating tap holder supposedly takes up the variances in spindle speed vs. feed rate. Tormach has a white paper that discusses a few tricks on using a floating tap holder (attached).

Reading through the list of parameter settings for my VFD (Hitachi WJ200) it appears that I do have control of spindle speed acceleration and deceleration. I'll play with these settings and see how it works out.
 

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Boswell

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It would be great to be able to tap on the Mill reliably. Good Luck !
 

spumco

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I guess I'm going to find out. The floating tap holder supposedly takes up the variances in spindle speed vs. feed rate. Tormach has a white paper that discusses a few tricks on using a floating tap holder (attached).

Reading through the list of parameter settings for my VFD (Hitachi WJ200) it appears that I do have control of spindle speed acceleration and deceleration. I'll play with these settings and see how it works out.
Tom,

I've attached my parameters for my WJ200-SF15. It's working rather well for me. Please keep in mind that I have a different motor (2HP Marathon vector duty with an encoder and a belt drive). The accel/decel work great - it's fairly aggressive but doesn't trip the breaker.

Don't copy everything, but these settings are working for a similar setup.


PS - I'm using UCCNC, so I can do rigid peck tapping using the motor encoder and a spindle index. Way, way nice. Not going back to Mach3.

-Spumco
 

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TomS

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Tom,

I've attached my parameters for my WJ200-SF15. It's working rather well for me. Please keep in mind that I have a different motor (2HP Marathon vector duty with an encoder and a belt drive). The accel/decel work great - it's fairly aggressive but doesn't trip the breaker.

Don't copy everything, but these settings are working for a similar setup.


PS - I'm using UCCNC, so I can do rigid peck tapping using the motor encoder and a spindle index. Way, way nice. Not going back to Mach3.

-Spumco
Thanks for the info. I have to look but IIRC my accel and decel settings are 1.5 seconds. Our setups are similar. I also have a 2 HP Marathon Black Max vector duty motor and belt drive. No encoder though.
 

TomS

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Finally had some time in the shop today. The lag at Z retract was due to the CCW Spindle Spin Up setting in Mach3. Changed it from 1 second to zero and no lag now. Here is a link to my media gallery showing the floating tap holder tapping six 1/4-20 holes in aluminum. http://www.hobby-machinist.com/gallery/albums/users/toms.24891/. I still need to fine tune the feedrate to reduce the amount of tension on the retract cycle but overall I'm pleased with the results.
 

Boswell

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That looks great. I guess this is hand coded
 

TomS

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That looks great. I guess this is hand coded
Today I tapped 135 1/4-20 holes in about 22 minutes. Hand coding this would have taken way too long and tested my patience. I use CamBam for generating gcode. With the help of another CamBam user I used a custom script he provided. I tweaked it a bit to suit my mill characteristics then generated the gcode file.

Here'a screen shot of a test piece I created and the script. I removed the dwell before the M4 command and changed the feedrate to suit my spindle RPM and thread pitch.
tapping forum reply (1).PNG
 

Boswell

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Here'a screen shot of a test piece I created and the script.
I used CamBam originally but eventually moved to BobCad. The sub-routine that you show above is what I was thinking would have to be custom. Looks very simple.

I can't imagine tapping 135 1/4-20 holes by hand or even with a hand drill.

Thanks for sharing this.
 

spumco

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Sweet.

I rigid tap, so I don't have a floating holder. Was just thinking you could put a little bit of stiff clay in the bottom of a few holes and then tap them. Check hole top to the top of the clay and that'll give you a ballpark on the over-run before the spindle reverses. I'm betting you could get pretty close to the bottom of a blind hole once you tested a few with some clay.
 

TomS

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Sweet.

I rigid tap, so I don't have a floating holder. Was just thinking you could put a little bit of stiff clay in the bottom of a few holes and then tap them. Check hole top to the top of the clay and that'll give you a ballpark on the over-run before the spindle reverses. I'm betting you could get pretty close to the bottom of a blind hole once you tested a few with some clay.
Thanks for the tip. Hadn't thought about blind hole tapping yet.
 

MontanaAardvark

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Finally had some time in the shop today. The lag at Z retract was due to the CCW Spindle Spin Up setting in Mach3. Changed it from 1 second to zero and no lag now. Here is a link to my media gallery showing the floating tap holder tapping six 1/4-20 holes in aluminum. http://www.hobby-machinist.com/gallery/albums/users/toms.24891/. I still need to fine tune the feedrate to reduce the amount of tension on the retract cycle but overall I'm pleased with the results.
I missed that this had morphed from a conversation on the flood coolant and breakout board problems into CNC tapping. I just tapped four 10-32 holes in my tooling plate and while I did more than you did in that video, each hole took longer than the six holes in that video.

How much do those tapping heads go for? I'm still working on changing to a spindle motor I can control from Mach3 (or whatever) - at least in concept. Adding tapping capability would be extremely cool.
 

TomS

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Yeah, this thread went off in a couple of directions. Sorry about that. Started out as a BoB relay wiring issue, then moved into a M3/M4 problem that raised it's ugly head when I tried to use my floating tap holder. Fixed that problem then after going through all of this I was finally able to test out my tap holder.

OK. Now to answer your question. My floating tap holder is a ER20 sold by Shars and bought on eBay. As I recall I paid $111 delivered to my door. It's actually a nice piece of tooling; ground on all surfaces and the tension/compression action is silky smooth. It takes a little adjusting to get the feedrate and spindle RPM to match up. In the video I had the feedrate set at 95% of the calculated feedrate per Tormach's recommendation. As you can see the tap was being pulled out of the hole. Not a big deal but it does distort the thread lead in somewhat. When I tapped the 136 holes I set the feedrate at 20 IPM, which is the calculated feedrate. I had minimal tap pull out and the thread was not distorted.

BTW - I'm using a PMDX BoB and spindle control card and a ethernet smoothstepper to control my spindle. Got this idea from jbolt.
 

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Having the reversible spindle has to be a big part of it. I noticed the spring action on the tap holder, but didn't know it wasn't intended.

Replacing the spindle motor is on my ToDo list for this year. Haven't spent the time looking for a BLDC motor, but I'd like to do something around 1-1/2 HP. 1 HP would be adequate. I'm pretty sure I'll need to replace my breakout board - I have a simple CNC4PC board and I don't believe it has any capabilities for motor control.
 

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I'm pretty sure I'll need to replace my breakout board - I have a simple CNC4PC board and I don't believe it has any capabilities for motor control.
I have an unused C23 board from CNC4PC that has on-board spindle control. It's NIB - just didn't use it as I needed different input voltage capabilities for my spindle encoder so I went with a different BOB. PM me if you want to upgrade your BOB.

I also have a "3HP" BLDC motor available much like the 'kits' sold through Automation Technologies. You'd need to find a driver for it but it was working fine when I upgraded to an induction motor. The reason I pulled it was the driver - which I still have - was junk, and the BLDC drivers that are available now weren't really proven a few years ago.

It's 5k RPM, and it's probably about 2 or 2.5HP once you discount the marketing lies.
 

TomS

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Having the reversible spindle has to be a big part of it. I noticed the spring action on the tap holder, but didn't know it wasn't intended.

Replacing the spindle motor is on my ToDo list for this year. Haven't spent the time looking for a BLDC motor, but I'd like to do something around 1-1/2 HP. 1 HP would be adequate. I'm pretty sure I'll need to replace my breakout board - I have a simple CNC4PC board and I don't believe it has any capabilities for motor control.
The spring action is intentional. It's purpose is to compensate for differences in spindle RPM vs. feedrate. If the difference is too great you get what shows in the video. It's not the ideal tapping method. I have to believe rigid tapping is the ideal method but the floating tap holder with a little finessing is a satisfactory alternative.
 

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I have to believe rigid tapping is the ideal method but the floating tap holder with a little finessing is a satisfactory alternative.
I don't know this from personal experience, but I believe the ideal method is to use rigid tapping with a tension-only holder. This permits peck-tapping as the thread starts at the same point every time, but also permits a slight amount of variation between the thread lead and spindle synchronization on retract. No over-run on entry so you can tap to within a few 'thou of a blind hole every time in all materials.

It's reported in a few places online that this method creates more accurate threads and the taps last longer.

If someone wants to send me a tension holder I'd be willing to give it a go...:)
 

TomS

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I don't know this from personal experience, but I believe the ideal method is to use rigid tapping with a tension-only holder. This permits peck-tapping as the thread starts at the same point every time, but also permits a slight amount of variation between the thread lead and spindle synchronization on retract. No over-run on entry so you can tap to within a few 'thou of a blind hole every time in all materials.

It's reported in a few places online that this method creates more accurate threads and the taps last longer.

If someone wants to send me a tension holder I'd be willing to give it a go...:)
I stand corrected.
 

spumco

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I stand corrected.
My comment was mostly just me being obnoxious :)

I think you'll be just fine with your current setup. You clearly didn't have any problems turning that aluminum to Swiss cheese.

The only time I've needed rigid tapping vs a tension/compression setup is with big taps. My spindle just doesn't have enough guts at 400RPM to push a 1/2" tap 1" deep in mild steel in one shot. Peck tapping at .250" per peck with a spiral flute was the only way I could get all the way down the hole.

If I had more horsepower down low, or drilled a bigger starter hole, or used a coated tap at higher speed it would have been fine.
 

TomS

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My comment was mostly just me being obnoxious :)

I think you'll be just fine with your current setup. You clearly didn't have any problems turning that aluminum to Swiss cheese.

The only time I've needed rigid tapping vs a tension/compression setup is with big taps. My spindle just doesn't have enough guts at 400RPM to push a 1/2" tap 1" deep in mild steel in one shot. Peck tapping at .250" per peck with a spiral flute was the only way I could get all the way down the hole.

If I had more horsepower down low, or drilled a bigger starter hole, or used a coated tap at higher speed it would have been fine.
My comment was mostly just me trying to be funny. Your response was informative and appreciated as they all are. My apologies.
 

spumco

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No need to apologize. I am the opposite of a special snowflake; more like rhino hide.

Now, if we're done with that, how about sticking a fork in this thread? Seriously, I'm having fits trying to get Fusion360 to do my bidding and I need some help. I'll go start a new thread and we can drive it off on a tanget...
 
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