Question for Iggy

I have been impressed by your efforts with your CNC mill. I would very much like a similar machine, but I am not at all sure a
similar effort is financially viable. So, the question is; Have you done a cost analysis of your project? If so, would you mind posting your material/equipment costs and your hours. Thanks in advance, Steve
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Steve, I have a spreadsheet here. The tab is "components used".
http://igor.chudov.com/projects/Bridgeport-Series-II-Interact-2-CNC-Mill/08-Spreadsheet/
You really need to read it carefully.
Please note that it includes the cost of 4th axis stuff, such as Troyke CNC rotary table, resolver converter, etc. Also includes a new PC that I assembled.
The mill's cost was $500, but I sold parts of it for $495, which is also reflected here.
i
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Ignoramus9343 wrote:

http://igor.chudov.com/projects/Bridgeport-Series-II-Interact-2-CNC-Mill/08-Spreadsheet/
Just remember to multiply the "Iggy scrounge" costs by 2.5X to get the real costs for the rest of us...
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On 11/30/2010 02:48 AM, Steve Lusardi wrote:

Iggy did not go the cheap route. He did it "right" according to my view, but he could have done it cheaper. If cost is real important, get a stepper-driven BOSS mill with a dead control. There are lots of them around. Build a power supply and get some Gecko stepper drives. Total cost for retrofit components will be about $300 - $500 depending on how good a scrounger you are. Admittedly I am pretty experienced with this, but I could get it running in one weekend. Many BOSS machines are 2-axis only, for a fully flexible machine you want to start with a 3-axis CNC machine, not with the 2-axis BOSS with the ghastly "spindle wizard".
Jon
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My 2.
Also, it depends on what you want to do, and how much of it you want to do ...
... and how much of it you really do.
If you just want to cut 2-3 small parts a year and maybe engrave a half dozen things. You pretty much can't beat a MaxNC5 from Deepgroove1 (Paul Henrick) for under a grand for price. The new ones have ACME screws and anti backlash nuts from Max NC. I would double check that the one's Paul buys from them are assembled the same, but I like the Gecko controller he provides much better than the Max NC controller. (Mine was a clapped out 10 year (atleast) old machine that I retrofit.) I like the construction and alignment of the MaxNC machines better than the Taig mills even though the MaxNC is all hard anodized aluminum with no iron parts.
I am doing about 10-15 times as much work on my mini mill(s) as I originally planned to do. Its one reason why I have experimented with multiple spindles, bigger motors, high speed spindles etc. Its also why I picked up the used Hurco. I hope I can get it going and set it up to cut 4-5 complex parts in a run... or more just by removing finished parts and replacing them with blanks while it cuts the next one. As far as the cutting time... I don't think it will be any faster. You can only push a .039" cutter just so fast.
I really like Iggy's setup. If I had it to do over again paired with all the hard won knowledge and experience I would probably still have started with a "turnkey" (note the quotes) mini machine. However, I would also have immediately started shopping for a good big machine to retrofit or repair. The mini machine is awesome for making parts for the bigger machines. It is possible to have everything you need to start cutting parts with a mini pretty cheap.
My next experiment is a laser / camera scanner to generate point clouds ... Yeah right. In about 5 years the way projects are stacking up. LOL. Fortunately there are lots of DIYers who have already done it.
Part of amount of work though is that I have found making chips is almost as enjoyable to me as fishing.
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My opinion only. Buying that Bridgeport Interact mill was NOT due to my foresight, deep knowledge of CNC, or careful analysis of what exactly I need. It was more of an element of dumb luck, combined with an insight that a machine of this size is manageable, yet capable.
Most importantly, I was VERY attracted by the fact that the machine did not seemingly need any physical retrofit (such as swapping lead screws for ball screws and other such things). I am now of a very firm opinion that doing physical retrofits is always suboptimal.
Knowing what I know now, I personally would stay away from any hobby machines.
i
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Yeah, and most folks don't get to buy a machine for $500 either. Heck anything other than full training by the factory service rep who just installed your brand new $100K machine with tool changer might be considered suboptimal by some folks. If I had gone that way or anyway other than at the lowest end I would still be out in the cold as far as making my own parts.

Fair enough, but how long did it take from the time that you bought your mill until you were CNC cutting parts?
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It is not like I was privileged in any way. It was not an inside deal. I saw the same ad on craigslist that everyone else saw.
So I had the same opportunity that was available to anybody.
I was not even very quick to buy it, it took me about 3 hours to finalize all conversations with the seller and arrive at a virtual handshake. If you recall, I was asking questions here as to whether to go with it.
Then I paid same evening and took possession of manuals and tool holders.

I think that if I was making money by machining, this is what I would do, as well.

I bought it in March around March 15. At the end of March, I picked it up and delivered to my friend's warehouse. I got it to my house around June 1.
On Jul 31 I made my first metal cuts (sprocket). So, it was 2 months.
I spent about 300-350 hours. If I billed someone for that at $50 per hour, the cost of my time would be $17k. However, if I paid $17k to get a working CNC mill, I would not have learned a lot of useful things.
On balance, unlike making a microcontroller control for a welder, it was worth it. The welder was the opposite, I spent a lot of time, and a lot of money, I ended up with a machine that worked as designed, reliably, but was inconvenient to use.
i
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Let me first say I don't disagree with your reasoning one bit. Just wanted to point out that from another perspective for a different person another machine might be a better starting choice depending on what they want to do. I think it was a better starting point for me. I have 100% confidence now that I can take a non working machine and turn it into a working machine. If I had started out with the Hurco two years ago though I suspect it would still be sitting under a tarp in the shop and I wouldn't have cut any parts in all that time. Instead I used the Taig to make parts, and even to make parts to take another small non-working machine and turn it into a working machine. I will probably use the two mini machines to make any parts I need to get the Hurco going too.
(I've even been playing with the idea of making mini machines for sale, but incorporating some of the things I have learned to make them better for the price.)
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Is there something wrong with this Hurco?
What is its condition?
i

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wrote:

I can't imagine buying a used machine and not assuming it has problems.
Problems:
1. Well, at the moment I haven't figured out how to get it off the trailer and into my shop where I want it. 2. Mechanically it seems sound. X & Y work. Z may not. If I can't get it going I'll just start retrofitting the electronics. I may do that anyway in order to get more modern PC based controls for it. 3. Need to pick up a rotary phase convertor for it.
If I retrofit to a newer control it I may want to do some things differently. Hence make parts.
Re: 2. There are a couple things I can think of to try after reading the manuals (IT CAME WITH MANUALS) that might cure the Z problem. It may be stuck in dry run mode mode. Z axis brake may not be releasing. Etc.

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    [ ... ]

    [ ... ]

    Just out of curiosity -- does it perhaps need compressed air to release the Z-axis brake? Make sure that you are supplying it with everything that it needs.
    Enjoy,         DoN.
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On my mill, no air means brake not applied.
i
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Ignoramus24652 wrote:

They're talking Z axis brake, not spindle brake.
On machines that have them, Z axis brakes are normally of the power/air/hydraulic to release i.e. fail-safe variety to endure the heavy machine head doesn't crash into the table/part/vise/fixture on power down. Small machines with Z quills don't have Z brakes since they don't have enough weight to cause the Z ballscrew to back drive when the servo is off.
Spindle brakes don't usually exist on larger machines with servo spindles and ATCs since they aren't needed. The spindle servo handles braking and spindle orient just fine, and the power drawbar is a spring loaded (belville washer stack) hydraulically operated setup that doesn't impart any rotational force when operating.
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I see. Thanks. In another life, I may want to be a CNC programmer or something of that sort.
i
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It does require compressed air. For what specifically I have not determined yet. There is a filter drier (cheap kind) on the back of the machine. and it specifically lists some air requirements in the manuals. I was thinking it might be for the lubrications system, but it would make sense to be for an air release brake.
I was thinking about all this stuff, but I am still cleaning up the shop right now to make room for it, and to get he trailer inside.
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wrote:

It's a good thing educational time isn't billable.

Suckage.
Congrats, Bob.

There ya go.

<both ears perked up and faced forward for that>
Yes, go on...
-- Do not taunt Happy Fun Ball!
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Well, some ideas you just have to go make some chips to learn what you really need to do. Some ideas you need to wrap your mind around for a while and then just go crank it out. Some ideas you need to do the 2nd first and then the 1st 2nd before going back to the 2nd before getting back to the 1st to make a real part. (Clear as mud right?) I'm somewhere in the middle. Fortunately all the other projects and ideas help with the hard won knowledge and experience of the chip making process. There are a number of approaches and cost is a major factor.
For example its pretty hard to beat a preloaded ball screw nut with some spring pressure on it. Ok... so just make it with top quality ball screws right with antibacklash preloaded drive nuts? Not if you have a price target. Top quality ball screws alone without the cost of the rest of the parts of the machine cost as much as some machines. At the opposite end of the spectrum are 60 deg V thread lead screws with simple brass (or bronze for more money) pinch nuts. Cheap, effective, and somewhat accurate ones can be had, but at the cost of long term life and accuracy and uneven wear making it more complicated as your machine ages.
How about using a combination of things for a compromise. Delrin wears very nicely, but it has a load coefficient that will destroy it pretty quickly once you go over it... once. Backlash reduction... elimination... Backlash nuts work, but many machines can apply more force than the springs can take and when pushing hard you can lose your compensation, although repeatability on the same cut will be decent. Beef up the spring? Then you are working your motors harder too. Get bigger motors you say? Then your price goes up.
I said was "playing" with the idea. LOL.
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Bob La Londe wrote:

Quality rolled ballscrews with minimal backlash, and software backlash compensation. Just keep the backlash to compensatable levels, and the drive system up to performing the compensation. Don't forget the pitch error screw mapping as well.
My little X2 mini-mill performs decently with it's stock ACME screws and bronze nuts, driven by 600oz steppers at 30 IPM which is a decent feed rate for a fractional HP spindle with a 2,500 RPM top speed. Even the much crummier Z performs surprisingly well with a stepper driving it's stock "fine feed". Certainly I could improve things, but I had about a week to get the machine running for a project and it's done quite well.
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Let me first say I don't disagree with your reasoning one bit. Just wanted to point out that from another perspective for a different person another machine might be a better starting choice depending on what they want to do. I think it was a better starting point for me. I have 100% confidence now that I can take a non working machine and turn it into a working machine. If I had started out with the Hurco two years ago though I suspect it would still be sitting under a tarp in the shop and I wouldn't have cut any parts in all that time. Instead I used the Taig to make parts, and even to make parts to take another small non-working machine and turn it into a working machine. I will probably use the two mini machines to make any parts I need to get the Hurco going too.
(I've even been playing with the idea of making mini machines for sale, but incorporating some of the things I have learned to make them better for the price.)
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