[MJ_cnc]

I'm considering buying an IH mill for prototyping in mostly plastic and aluminum. To help pay for it, I might be able to get some work doing various production runs in plastic for a company I know. The issue is the tolerance is really, really tight.

The production run consists of 300 to 500 parts in acrylic plastic. Dimensions are .3" wide x .160" tall and range from 2" to 6" long. Down the length of the part is a groove. The groove is 0.072" wide by 0.036" deep. I've attached a very ROUGH sketch.

Tolerance required. This is the TRICKY part. The drawing calls out standard tolerances, but IP (Inspection Protocol) is ridiculous and holds much tighter tolerances.

The actual 0.3" wide has to be between 0.299 and 0.297 so that it can 'easily' slide into a tool holder for production. If it's a tight fit, or too lose, it's rejected.
The 0.160" height has to be slightly undersized between 0.1595" to 0.158", again to fit into the tool holder. This is where issues come in because two parts are placed together and if they're too tall or short, the total (0.160+0.160 = 0.320") dimension issue is magnified.
Lastly, looking at the groove, it needs to be .036 to 035 deep or it won't do it's job correctly.

These are currently made on an older 199x FADAL VMC. It's done by using a larger piece of acrylic, approx 14" x 9" (guessing on this one) and double sided sticky taping it to a plate mounted to the table, and cut as many as we can depending on the 2" to 6" length. We cut down to the tape and then 'pop' the parts out when finished and clean up.

My question is - can I make this part repeatably on an IH CNC setup? I've read in http://www.cnczone.com/forums/showpo...7&postcount=52 that ksanalytical thinks he can do better than +-0.001 in the Z. Based on that thread, it's a matter of spending the time to make sure I setup the machine correctly. Any thoughts?

Thanks in advance,
Mark

[Cruiser]

The machine if properly adjusted, is capable, If the man on the controls has the technique to make it happen ! There are many varyables to contend with that can and will effect tollerancing.

[ViperTX]

Mark,

Unless you're buying a turnkey system with demonstrated x and yaxis perpendicularity...I think you're opening yourself up for a major headache.

In you're drawing I did not see any tolerances regarding perpendicularity...surface finish...and etc.

Paul

[Runner4404spd]

Can the machine do it? yes absolutely. can you setup it up so that it can do it within a reasonable amount of time? maybe. the biggest hurdles you will run across and its pretty much with any import machine tool is whether or not the home has the tool to properly setup a machine. for one, that includes making it level? this is not done with a simple bubble level from lowes or home depot. you need a precision level that will run about $750.00. then you will need to square the column to the table and then the spindle to the table and finally you'll be at a point where your ready to make some parts. and thats assuming you bought a ready to go machine and even then there maybe some issues with gibb adjustment that may need to be addressed. for milling acrylic i think you would need a higher RPM spindle than what comes on the machine. so theres another upgrade that you need to do. and once you do that you'll find the chinese spindle bearings are inadequate, so you'll need to buy a set of angular contact bearings. and you'll probably burn up the first set figuring out the preload.

is it doable? absolutely, after a few years of futzing with mine, its finally to that point where i could machine those parts and hold those tolerances. it was a good learning process, but don't expect to buy a bench top cnc from anyone, drop it on your floor, and start making good parts that are to print.

[MJ_cnc]

Thanks everyone for the response. Your feedback is pretty much along the same lines as I've been thinking. The example part that I posted is the toughest part I can think of at this point and will have to fall into the category as 'nice' to have.

It's all about trade-offs. Do I spend the time (head-ache as Viper says) to fine-tune an IH or look to something that costs more $$ and less head-ache. It's hard to justify more $$ and it is not easy or impossible to fit a larger mill into my garage with limited space and power requirements. The travel (30 x 12) of the IH and potential is attractive. I do realize that ksanalytical does not get the same specs over the whole Y' travel, but I certainly don't need that if cutting smaller sizes.

I'll keep reading everything I can about this mill and a few of the others. I started reading the lapping vs. scraping thread and that hurts my head.

Thanks,
Mark

[Runner4404spd]

honestly your best bet for something ready to go with a tool changer that can fit in your garage is a haas mini mill. it may not fit your budget however, next after that would be a fanuc robodrill, again not really garage friendly and can be size and budget killers.

[MJ_cnc]

I just looked at the Haas and Fanuc online and they are a thing of beauty. Ebay has 2 haas mini-mills for sale. Fantastic machines.

Found another: http://www.meridianmachinery.com/cncvmc/2054.htm

I don't think either would fit in my garage unless you tipped them significantly (on their side?) and I can't see that happening w/ a 3000lb to 4000lb machine. My garage door when open is only aprox 6' 6" high. Even if I remove the door, I'm closing in on 7'. No-way a 98" machine on a handtruck goes in there unless we get a Jedi Knight. (Hmmm, maybe the Z-axis can be all the way down or taken off?? Will have to investigate.)

Also, I still need tooling, accessories, etc.

I need to sleep on it (for several weeks+), but I'm leaning towards the head-ache at this point because of the cost and size issues. One thing this discussion did was change my mind from a turn key IH to buying the manual plus the cnc kit. It's slightly less $$ ($3.2K + $4.5K = $7.7 vs $10K) and I can put together the electronics no problem. If I need to take the machine apart to work on it, I might as well take the whole machine apart and reassemble it and become familiar w/ it all. My real job is putting together (mostly specifying now) automation systems. Doing a Mach 3 setup w/ servos or steppers is well within my comfort level. I'm actually weaker on the specifics of machining and the mechanics. but, with time and help, I can learn that.

Mark

[doorknob]

One thing this discussion did was change my mind from a turn key IH to buying the manual plus the cnc kit. It's slightly less $$ ($3.2K + $4.5K = $7.7 vs $10K) and I can put together the electronics no problem.

Just a note of caution - there have been several reports on this site of people ordering the manual IH mill plus the CNC kit having extremely long wait times, missed schedules, and unmet delivery promises, while others who have ordered the turnkey mill have supposedly gone to the head of the line.

I do not have any direct experience with either version.

[MJ_cnc]

Have read the thread about 'Return my money.' I think at this point, I am willing to wait. So might be a good fit.

Just a note of caution - there have been several reports on this site of people ordering the manual IH mill plus the CNC kit having extremely long wait times, missed schedules, and unmet delivery promises, while others who have ordered the turnkey mill have supposedly gone to the head of the line.

I do not have any direct experience with either version.

[ksanalytical]

Mark,

We seem to be in similar situations. I personally went with IH because I wanted to be able to spend time on these projects at home rather than spending all my time at the shop. Frankly, the IH is the biggest thing that would fit. I have the IH mill, a 12x36 lathe and an AC Cobra kit car sharing a single garage bay and I can work on either machine tool without breaking my neck.

The comments I made about sub 0.001" Z moves were based on surfacing cuts of ~0.0005". Basically, that machine has shown itself capable of "relative" moves that small, but whether or not it can do it with larger DOC or after plunging into the face of the material, I don't know.. I'm personally finding out how much more complicated things become when you just set a depth and tell the machine to run. My part has a circular pocket in the middle which would ideally be 0.002" deep. These are being run on a plate that I surfaced, then started using without unbolting it so flatness of the table should be a non-issue. The wells (prototype production is just two at a time side by side in X) are only separated by ~2" and the plates are bolted down with 1/4"x20 bolts at the ends and one between the two parts (both machined out of a single strip of Al). I've run three sets so far with variations in the actual depth from 0 (tooling marks fade to nothing right at the edge of the pocket) to 0.005".

Surface finish has also been a real challenge. I travel a lot, but my next project is to try and smooth out the edges without slowing it so much that it rubs. I suspect this is a rigidity issue and as such, might be beyond the "easy fix" level.

It's quite likely that part of the problem is my height setter as it's based on a simple chinese dial indicator, but I also have noticed that if I move the Z down onto the height setter and pull down on the spindle, I get about 0.005" of movement that does not recoil (like column flex). I don't think it's backlash because I can move it both directions with relative ease and pressing on the head causes less movement and it returns after I stop pushing. The best I can tell, it's some kind of vertical play in the spindle. I've been suspicious of my spindle bearings recently as they seem to be making more noise so that might have something to do with it.

Lastly, I'm not a machinist. I'm completely new at this and learning as I go. I believe these other guys when they say that it's possible, but I've proposed tight tolerance jobs like this in Al to other pro machinists who simply told me that it's not possible to maintain sub 0.002" in Al. I can only assume acrylic would be even harder to work with. My tolerances aren't really that critical so the IH is working well for me. The way I see it, you can blow $25,000 on a used pro machine right now to fit the tolerances for one job, or you can get a machine that fits YOUR needs and YOUR space for a lot less.

I hope that helps and feel free to ask any addition questions about my experience.

Ken

[Cruiser]

As for the turn key or do the work yourself, I feel that the turn key is going to be much more $ friendly in the long run and be much quicker to get adj'd and tuned in.
As for the finish with an end mill, I have found that even some of the high $ carbide end mills are not perfectly square on the end and leave a bit of a step, and changing to a known square end mill leaves a perfect surface finish. That is with my quil set to within .001" within a 6" swing using a plate on table. I have been only buying carbide end mills lately and tried a number of brands, some are really good and some are only tolerable. I think it all depends on the truing of the grinder that makes them, and how long they run in between truing.

[MJ_cnc]

Ken,

Thanks for the feedback. I have read you thread on 'New IH on order' in it's entirety and several sections of it more than once. Good Stuff.

I'm tending to agree with you, spending $20K+ on a machine at this point is not something I can justify. I drool over the Haas Mini Mills that are posted on the cnccookbook, but that would be phase III...

I do agree the turnkey is an easier way to get going, but from what I've read, guys are pulling their machines apart and lapping (or scraping) and replacing various items. If I need to pull it apart, then I might as well do the retro fit. But, along the lines of Cruiser's comments, it's a catch 22, how do I make parts for a retro fit when my machine is apart? I do have limited access to a shop at work, so that might be an option.

Putting together the electronics and Mach3 is no problem, that's the type of work I do during the day. It's the bearings, lead-screw, and nut mounting that I would have to work through. After looking at pictures, I'm thinking, "It's not that hard." Famous last words...

Anyway, I'm getting ahead of myself. Talked w/ the wife last night and her question was, "Where are you going to put it!??" I need to clean out that side of the garage and get Power run to the garage. I have a cheaply built house w/ ONE 115Vac outlet in the garage. So, realistically I'm a couple months away from worrying about turn-key vs. retro.

Mark

[universalfab]

Save your money and have somebody make your parts, like us...

[Cruiser]

This reminds me of the guy at work who mortgaged his house to buy a mazak and now he don't live there any more.