jig grinding on CNC Mill

[rdavidson]

Good morning everybody,

 

I am wondering if anyone does any jig grinding on a CNC mill? Occasionally I need to grind button holes after heat treat and all wire EDM work is completed. It seems to take me too long to grind the holes to size. My request is for any information that would make this task more efficient such as: types of grinding wheels, speed, feed, ect. My procedure is to program a boring cycle, use a boring head with an air-operated jig grinding attachment and a borzon wheel mounted in it. I will use a programmed speed of 400rpm and a feed rate of 15.0ipm and override as needed. After the program is processed, I will copy and paste the location of the hole about 15X, use a G99 to shorten the travel and program the tool to exit the hole on every pass. I am using MCX3. Generally, the hole sizes range from about .500 diameter to 1.000 diameter. Thanks for your input.

 

roger

[Matt Berube at Ferron Mold]

It's been a while since I've done any jig grinding and I've never tried it in a CNC mill.

 

Borazon wheels sound like a good choice. Feed & Speed sound OK too...

 

I have to wonder how fast the air spindle goes. I am thinking that a faster air spindle is the only way to speed the process unless you can reduce the amount of material left to grind away.

 

How long is it taking to finish a hole ?

 

Are these blind or thru holes ?

[rdavidson]

Matt, thanks for the reply.

The grinding head is rated between 50,000 and 65,000rpms. Sometimes it may take 30min to an hour to get a hole to size and to make sure it does not bellmouth at the top. Can you enlighten me on how to choose grinding wheels (finishing; roughing; grinding on the bottom; anything that I have overlooked??)? Most of the time the holes are for die buttons. There is a through hole, but it is a smaller diameter.

 

roger

[Matt Berube at Ferron Mold]

Grinding to a shoulder can be a nuisance.

 

Bell mouth should never be an issue. I would rough to near finish size then let it spark out completely, measure hole size and make final size adjustment and let it spark out completely again.

 

I don't recall the manufacturer of the wheels we used or even how rough the wheels were but I'd recommend using the largest and coarsest wheel you can get away with for the given situation...

 

When chasing a bell mouthed hole in the jig grinder I would often manually over-ride the up/down stroke for several passes to keep the tool focused wherever the material was remaining. Easy in a jig grinder... A nuisance in the CNC mill I'm sure...

 

How deep are these holes usually ?

[Mike-T]

I've always wanted to do this, what about coolant filtration ?

[Guest CNC Apps Guy 1]

^^^ Yeah, you BETTER do it!

 

I usually see guys get filter "paper" and the coolant dumps onto that before going into the tank.

[Kevangel]

Ok, I have 2 Yuasa air spindles the same range you have for use in lathe, mills, Moore Jig Borer before I bought Moore Jig grinders and this is gonna be waay slower than in a regular Moore jig-grinder. Moore Jig grinder #3 or G-18 (double V ways models) sell for 10K or less now at auctions fairly regulary...not like 10 years ago 40K or more, so may want to pick one up and with a read-out already on it.

 

Biggie ....Use carbide mandrels!! won't deflect. How much stock is in the holes? Can you rough carbide mill the hole first since you already are in the CNC Mill and just leave .002/side to clean up. Those small spindles do not have the power and torque for roughing like a regular jig-grinder....I have 2 Moore jig-grinders NOW and it is like being in heaven after using what you are using my whole career....no more looking thru a magnifying class at boring head adjustment screw trying to guesstimate and holding my breath on.0001/side sizes..Moore jig-grinder graduations are .100 inch apart for .0001/side and don't shut spindle off to do it..

 

grinding on bottom is always a pain in the arse and leave almost NO stock there, just kiss or carbide mill bottom!!!!!!!!!!!!. Moore Company has lots of wheels at web page.

[Kevangel]

quote:

---

The grinding head is rated between 50,000 and 65,000rpms

---

I am assuming this is an air model...maybe switch to an Yuasa elecric model may help....again regular jig grinders go cheap at an auction and one is being auction in dayton,ohio tomorrow

 

http://www.thompsonauctioneers.com/SHERMAN...INC-a137675.php

[Kevangel]

http://www.mooretool.com/

[nine blue]

Don't believe you are running enough RPM's.

Most grinding wheel manufactures recommend a general range of 6000 to 7000 surface feet per minute.

 

Based on the hole sizes you gave a 3/8 wheel would need to run at 66000 RPM and a 7/8 wheel at 28000 to obtain optimal metal removal.

RPM = (SFM x 3.82) divided by DIAMETER

 

Could explain the long cycle time to get it out to size and the bell mouth condition.

 

The 6K to 7K is only a general recommendation. You need to find out from your wheel supplier what they recommend for SFM.

 

Also borazon wheels are hard on your dressing diamond. Dressing diamonds ain't cheap.

 

You can certainly grind at 400 RPM but I believe you will experience excessive wheel wear.

[Greg Williams]

I have done a bit of this, Normally I just use a borazon wheel in the spindle with it running @ 15K and use a heix bore toolpath with a bit of hand editing

[Kevangel]

quote:

---

You can certainly grind at 400 RPM but I believe you will experience excessive wheel wear.

---

That is his spindle rotation, wheel RPM is 55-65,000.

[rdavidson]

Wow guys! I thank you for sharing your experience. I haven't considered filtering the coolant no more often than I have this task to come to the table. I have been roughing the holes with a carbide endmill and a helix toolpath but it seems that I need to leave less stock in the holes. This is good food for thought. Thanks again.

 

roger

[Kevangel]

Moore jig grinder above link..$4,750 plus 12 percent buyers premium...had readout..A steal, pathetic what country has come to..oh well..

[Odell]

We do Die button holes here every day and always hard mill them to size. I don't think we have ever ground a button hole. I have never use our C.N.C. for a jig grinder but I have on occasions used it as a surface grinder. Made an arbor for a 4" cup wheel and run it 3600 rpm.