[SWATH]

Don't waste your money on an import, they aren't accurate and they don't stay put. Go to ebay and find a nice Criterion DBL202, it will outlast you or the machine and it will be accurate. They make a lot of even better boring heads, but unless you are talking .0002" tolerance, they aren't necessary.

Thanks I'll do that!

[SWATH]

Ok Here is some very useful info I got from Phil especially if you use Gwizard. Most of you probably already know this but the the HP of the spindle is linear and it peaks at 3hp when at 5000rpm (machine programed max). So if you use the newest 1.6 version of Gwizard there is a function in the machine setup tab where you can input this info. The feature is called spindle power curve compensation. For the Mikini you can enter the low range at 200rpm (minimum) and high range 5000rpm (maximum), then you can put the peak at 5000rpm and 3hp. It will then scale your hp value when you are using the speeds and feeds calculator.

Here is the write up of this feature in the latest installment (ver. 1.6 10/31/11):
CNC Cookbook: Software and Information for Machinists

[SCzEngrgGroup]

Don't waste your money on an import, they aren't accurate and they don't stay put. Go to ebay and find a nice Criterion DBL202, it will outlast you or the machine and it will be accurate. They make a lot of even better boring heads, but unless you are talking .0002" tolerance, they aren't necessary.

Not sure what you're basing this on. I'm pretty sure you have not tested ALL import boring heads. My Enco is an import, and it works just fine. It's perfectly accurate, and it's always stayed put, and I've used to to bore to a few tenths with no problems whatsoever. They all have locks on the gibs, so I really don't see how they could NOT stay put when used properly. A boring head, after all, an exceedingly simple mechanical device....

Regards,
Ray L.

[Brian L]

Basing it on 40+ years of machine shop experience and owning many a Criterion, and a few cheap imports. Yes, I am sure not every import boring head is garbage, but a nice huge percentage of them are.

It is not an exceedingly simple device if done properly, the threads on the screw need to be ground, the female thread should be lapped. And you never, ever, lock the gibs down to hold the boring head in place. You use the gibs to supply a nice consistent tension on the head, relying on the tension against the screw to hold the head consistently, otherwise how would you ever make a .0005" adjustment? Unlock the gib, turn the screw a half thou and lock the gib back up, yeah, that'll work.

Why waste your money on cheap Chinese crap when for about the same $100 he can buy a decent, made in America tool that will actually do the job, and do it reliably for years to come.

[SWATH]

What do you guys think about this one? I don't know what the A stands for but I guess I would need an R8 shank and some boring bars.

CRITERION BORING HEAD #DBL-202A #25200 W/ ADJUSTMENT | eBay

[mcphill]

How about this one?

Criterion USA Mod 1 1/2 USA boring head tool tools | eBay

[Brian L]

Keep looking, the one Swath pointed to is good, but it has the tenth set ring on it, most likely more money and precision than you need, also adds some length to the whole thing. After looking over ebay, that's probably your best shot.... or wait.... I tend to be cheap and don't mind waiting until I score a deal.

The second one is an old square head, actually more rigid than the round head models, but they don't have the offset second hole or the cross hole, so you are much more limited in size range... you only have what the head will travel, so you have to have numerous different sized bars to cover a range. Another issue with the square heads is they get out of balance real quick and can make the whole machine wobble at anything but a slow rpm.

Given the scarcity of the DBL202's on ebay they must be pretty popular, stay with the owners. Oh... search CB-202, Criterion has discontinued the DBL's, you can buy a brand new one for $290.

[SWATH]

I ended up going with this Criterion DBL-202B set from Enco:
Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies

If you use the code HPRNOV you will get 15% off till the end of the month.

It comes with the 2" dbl-202B head, a Criterion R8 shank, and a an 11pc C6 carbide boring bar set, all for $237

[SWATH]

I have a couple of questions for you guys.

1. Does the Mikini support no drag boring? This is where when a boring operation is complete the spindle stops at a specific orientation then then moves the boring bar away from the surface of the bore before it retracts. Of course in order to do this the machine needs to know where the boring bar stops or it will crash it into the bore. I would think so if it supports rigid tapping and has encoder feedback.

2. How do you set up soft limits on the Mikini in Mach?

3. How does the G54 fixture offsets work in Mach on a stepper motor machine with non-precision home switches?

[kenealym]

Swath,

Don't know about drag boring but Phil says rigid tapping is supported with EMC - it is not supported with Mach3.

Config/homing limits in Mach3 lets you set up soft limits - from memory you need to toggle the "soft limits" button on (below the DRO boxes) for them to work.

I haven't used multiple offsets on the Mikinimech but I have had to opportunity to re-reference all axes then use G28 to get back to the zero on my job after I shifted the axes in manual mode with the pendant (don't ask why!) part way through. I wasn't expecting it to work but I got back to exactly the right spot and finished the job. It was a press fit right off the machine so even though the limit switches may not claim to be precision either they worked or I got lucky. Probably worth a test on your machine.

[dirtridn2010]

I have a couple of questions for you guys.

1. Does the Mikini support no drag boring? This is where when a boring operation is complete the spindle stops at a specific orientation then then moves the boring bar away from the surface of the bore before it retracts. Of course in order to do this the machine needs to know where the boring bar stops or it will crash it into the bore. I would think so if it supports rigid tapping and has encoder feedback.

2. How do you set up soft limits on the Mikini in Mach?

3. How does the G54 fixture offsets work in Mach on a stepper motor machine with non-precision home switches?

If i could just offer my opinion on Q1.
The Mikini does not support "no drag boring" because there is no ability of the machine to know where (as you mentioned) the boring bar has stopped. There is no spindle orientation on the mikini because it does not need it (no tool change etc.). With regards to Rigid tapping my understanding is that the tapping method used on the Mikini is to use a tension/compression tapping head. That way they only have to worry about the distance travelled by the Z axis (after the spindle has reached the programmed RPM) during the operation which is set within the program. Remember too is has a relatively slow startup time (probably due to the low torque (as previously discussed) at lower RPM.

Q 2and 3. Beats me

[SWATH]

The Mikini does have encoder feedback and will do rigid tapping (with the right control software) so I would think no drag boring would be supported. Here is what Phil said when I asked:

Q: Does the spindle do rigid tapping?

A: Yes, it has encoded feedback for rigid tapping. It requires user setup and
interfacing to EMC2 (Mach does not support it yet).


Q: What is "spindle position orientation"?

A: Encoding of the spindle for tapping above. Not offered on most benchtop
machines. Typically a option on industrial machines.

I'm just not sure how to set it up.

As far as soft limits, I understand how to turn them on and everything but what values to you enter in the min/max range in Mach for the Mikini? Do you have to manually measure where the switches are and enter in that value minus some? How does Mach know where the switches are in the other direction (other than the home switches)?

With the G53 stuff, Mach always asks me if I want to fixture save when I close it down. Not sure what that means but I think it means to retain my zero position as a G53 offset or something. Which makes me curious how the G53 offsets work. Are they saved fixed locations like a vice corner that can be referenced when the machine is referenced? If so, would that not require precision home switches? The Mikini manual states that they are non-precision and should not be used as such, indicating is required. Ok, so then what's the point in having them if they are useless. I've been thinking about this because I have to re-index the part every time I shut down and start up which is a pain. I thought if G53 will save that location then that would save a lot of time. Am I wrong about this?

I still have not received a fix from Mikini about my spindle RPM not being able to max out but I have confirmed another problem. It is nothing new and others have reported it but it sucks none the less. The spindle will not achieve correct RPM unless from a dead stop. For example, if the spindle is stopped and I MDI an S800 M3, it will go to 800rpm. However if I then MDI an S1000 it goes to something like 761 and the DRO kind of flickers 761-762. Then if I MDI an M5 then an M3 it goes to 1000rpm. That is frustrating because when you have a program that required multiple spindle speeds I would have to manually enter an M5 after every speed since my CAM software assumes the spindle will reach the right speed so it just goes from one speed to the next.

[Brian L]

I can't answer much in regards to the Mikini with it's home switches, but a friend runs an old Shizuoka ST-N with steppers and Mach 3. It doesn't have handles, but it does have dials on the end of the ballscrews, so you can set them to be zero when the machine homes. We have checked his, and it just uses simple proximity switches, and it homes repeatedly within .001" (as best we can see on the dial, probably better than .001").

Pretty simple to find out, home your machine, set the "machine position" to zero's. Go indicate in a bore on a part in your vise, write down the readings. Shut it down, start it up, re-home, MDI the readings you wrote down and re-indicate the same bore. If the machine keeps coming back to the bore, you are good to go. Honestly, I have found most stepper run machines with decent homing switches to be pretty accurate.

Then you can save that XY value in G54, or enter it into your program, or just MDI to it the next time you turn on the machine.

Fine boring... well, write a sample line of code and run it.... if the spindle has an encoder, it should work. It will stop the spindle, jog it slowly to orient it, then retract the amount you specify, then pull out, use exaggerated amounts on the pull back so you can see it in the air when it does it. This of course means you need to orient the spindle, install and clamp your bar so it's pointing (usually X minus) each time.... not so easy on a machine without drive dogs and a power draw bar (like my 40 taper spindle).

Soft limits in Mach 3, not real up on that, but you usually have limit switches at each end of your travels, say you have home at X0, other end of X travel is say 16", you would usually set the "soft" limits for maybe .250" from the hard limits, so the machine stops before it crashes anything that could get damaged. Not exactly sure how those work when you use proximity switches.... my machine has a two button switch, hard limit switch dogs at either end of each axis, with a second trip dog hitting the other switch for home. So home would be machine 0, soft limits would be say x-.25 and x16.25, with hard limits (the proximity switch) set at x0 and x16.

This way if you have a failed limit switch, if the machine ever gets more than 1/4" past the supposed limits it will shut down, a fail safe , if you will. Of course the machine would also have to have the ability to move that extra 1/4", make sure you aren't at the end of the stroke on the ball screws or way travel... don't want anything had hitting something else hard.

[mcphill]

I had a hard time with homing switch settings as well. Here is the thread on my discussion:

http://www.cnczone.com/forums/mikini...solutions.html

I didn't record the final resolution... I will add that to the post when I get back home.