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06-18-2009, 11:23 AM #1
Moore Jig Grinders - Schooling Needed
Can someone school me on Moore Jig Grinders? I am in need of putting in some close tolerance +/-0.0001" 5/32 dia stepped dowel pin holes in hardened steel.
I am looking at a used grinder that comes with a 40,000 rpm head. What else is needed to make this machine run? I see all kinds of tooling available on Ebay but how much is really needed? Where are the stones purchased from? Are they specially made for jig grinding? How are they dressed? There are different RPM heads out there? What RPMs are used for different sized holes.
06-18-2009, 12:12 PM #2
Unless you are starting a business which will rely on jig grinding you are going to incurr a tremendous expense for some holes. Most shops around here send the JG work out as it's cheaper than tooling one up. The most important item besides the grinder is a very large CFM moisture free air source. Wheels are the least of your worry. These days plated and unplated borazon and or diamond wheels are available. I have thought about getting a JG as well having run one for many years when I was in the trade. The expense far outweighs the usefulness when there are so many sitting idle in shops around the city. -Mike
06-18-2009, 01:25 PM #3
Thanks for this, Holescreek. I had just found out, on this forum, about the existence of jig grinders a week or so ago, and I was wondering, "how is it I had never heard of these before? And why aren't they a more prevalent machine tool?" I did a little research and talked to a guy who had run one, and they sure looked like they'd be sweet to have. I was wondering what the catch was; now I know.
06-19-2009, 07:04 PM #4
It cash flowed out for us because of the high cost on a few production parts. 1 inconell part that we were paying $75 per hole outside we got to run at almost 3 pcs. an hour in house. A second part cost $36 each outside to grind a hardcoated alum. slot, we run 10 pc.s an hour in house. A few more parts with savings like this justified the machine with about 20 hours of load a week. I didn't need to justify the compressed air because we're a large shop that has mutiple screw type air compressors that could keep up with demand. I did have to have this machine plumbed with it's own line to keep up with it's demand.
Another thing working in my favor was a new rule the company made that all vendors must be ISO certified and none of the local jig grind shops were. (We're in aircraft)
Otherwise, grinding points, wheels, arbors, dressers are all readily availible. The "workhorse" head from Moore is the 40K head. They have a wide range of others but unless you have a high quantity requirerment you will be done with the job with the 40K head before you'll have the head changed out to another. The exception might be if you are grinding a hole under .030 in dia. You might need the 120K or 175K head for that.
06-19-2009, 08:15 PM #5
The reason they are not more prevelent is because there are really very few situations where this level of precision is required. Unfortunately, a lot of engineers have never heard or do not fully understand geometric tolerancing and dimensioning (GT&D) and the costs associated with not applying these principles.
In most cases if two parts must be dowel pinned together and no clearance is allowable for a tolerance attainable with common machine tools, it is usually more practical to pin the two parts at assembly.
06-19-2009, 08:16 PM #6
At one point in history the shop I worked for had the most Moore jig grinders both in one room and within one company. (This was in the '80's). We had 50 running in one room in the main plant. Hardwood floors, red carpet runners between rows and a loaded Moore bench behind each one. Almost all had a nice moore rotary table on or sitting next to it. We had to start out by just grinding holes for the first year. When I started in the room we were just making the switch from stone wheels to the plated stuff ('82?). If you showed apparent skill you progressed to contour grinding and the best learned to jig mill. I went through all of the processes and onto running 2 CNC jig grinders in the middle of my second year. By the time I worked in there 3 1/2 years I was going stir crazy. Something about working in a noisy room without a single window looking at the same people year after year. That's when I escaped and moved onto the DeVlieg horizontal boring mills. Best move I ever made. -Mike
06-19-2009, 08:37 PM #7
IMO wire EDM has replaced jig grinding in many applications. We have both and if we have dowel holes and other through shapes, we do the whole thing with wire EDM. If they are blind holes, we jig grind. Non conductive, we jig grind. RJT
06-19-2009, 08:55 PM #8
06-20-2009, 05:06 AM #9
I would guess most job shops and larger these days already have at least 10 HP compressor, so it seems to me that unless the jig grinder user is wanting to run the grinding head nonstop more than a couple hours a day this would not be all that much of a negative.
06-20-2009, 08:14 AM #10
WRT the OP, if your sole interest is this one job, farm it out, the costs involved in acquiring the machine, tooling, and learning to use it well outweigh by a large margin what you'd save.
06-20-2009, 01:10 PM #11
Thanks for all the replies guys. I am trying to pull as much work inhouse as possible that's why I am looking at this guy.