What are Reasonable Goals for Home CNC?

This forum is dedicated to those Hobbyists Interested in CNC machining & 3D Printing in their home shops. (Digital Read Outs are also topical, as is CAD/CAM as it relates to CNC)

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magic9r
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Re: What are Reasonable Goals for Home CNC?

Post by magic9r »

SteveHGraham wrote:
I have used the compensation tool, but it's not that great.
Steve,
I have it set up on a mill and it works perfectly, if your backlash movement is very free then the compensation will not be particularly effective as the forces on the tool will still be able move the tool platform around within the backlash envelope during some cutting operations,
Regards,
Nick
WJH
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Re: What are Reasonable Goals for Home CNC?

Post by WJH »

I never played with a CNC machine, so take what I say accordingly...
Steve, you seem to be the kind of guy that loves machinery, can appreciate fine machine work, and loves power tools. Perhaps your struggling to figure out what to use a CNC machine for, well, because you never actually had a need for one, you just want one.
When I make parts for a live steam locomotive, i love making "one off" parts. When I am cutting wheels, with many operations, and I have to repeat it 8 freaking times on a manual machine, it no longer is fun. Right there is a use for a CNC lathe, making multiples of a part that would bore you to death otherwise on a manual machine after the first one.
Steve, are you a builder? Or a collector? If your a collector, that's ok, and accept that you may not really have a need for it.
Now, are we talking about converting your mini-lathe for CNC work? You can spend a fortune on quality parts for a CNC conversion, might as well have the machine match the quality of the components you buy.
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SteveHGraham
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Re: What are Reasonable Goals for Home CNC?

Post by SteveHGraham »

I would be in trouble if I could only keep the tools I need. If I asked myself exactly what I wanted to do before I bought a tool, I wouldn't have a mill or a lathe, because I didn't have clear goals in mind when I got them. I just knew that I wanted to have some chance of succeeding if I got an idea for making something.

A CNC lathe would be extremely useful for threading, which is a fairly dull job that offers a lot of opportunities to make mistakes. Also, a CNC lathe would not be limited to the threads available on my manual lathe or in my tap and die set, and it wouldn't be limited to right-hand threads. It can also be used to make balls. It would make tapers that work just fine, without a tool post grinder. It would be nice for any shape that involves curves.

Also, sometimes you will make a part that has a thin section and a fat section, so to make the thin part, you have to make a thousand passes to get rid of material. A CNC lathe will do that while you drink coffee.

On the whole, though, I wish I had a mill. I could use it to make fork clamps for a bobber/cafe racer project, as well as other parts. I could use it to make guitar bridge parts. CNC mills make all sorts of wonderful stuff.
Every hard-fried egg began life sunny-side up.
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SteveHGraham
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Re: What are Reasonable Goals for Home CNC?

Post by SteveHGraham »

I think my most extravagant buy was the plasma cutter. I had cut a few things using a dry saw, a band saw, and a grinder, and I kept thinking how sweet it would be to slice things off in a few seconds. I haven't used it much, but when you need it, there is no substitute. I love it.
Every hard-fried egg began life sunny-side up.
WJH
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Re: What are Reasonable Goals for Home CNC?

Post by WJH »

SteveHGraham wrote:I would be in trouble if I could only keep the tools I need. If I asked myself exactly what I wanted to do before I bought a tool, I wouldn't have a mill or a lathe, because I didn't have clear goals in mind when I got them. I just knew that I wanted to have some chance of succeeding if I got an idea for making something.

A CNC lathe would be extremely useful for threading, which is a fairly dull job that offers a lot of opportunities to make mistakes. Also, a CNC lathe would not be limited to the threads available on my manual lathe or in my tap and die set, and it wouldn't be limited to right-hand threads. It can also be used to make balls. It would make tapers that work just fine, without a tool post grinder. It would be nice for any shape that involves curves.

Also, sometimes you will make a part that has a thin section and a fat section, so to make the thin part, you have to make a thousand passes to get rid of material. A CNC lathe will do that while you drink coffee.

On the whole, though, I wish I had a mill. I could use it to make fork clamps for a bobber/cafe racer project, as well as other parts. I could use it to make guitar bridge parts. CNC mills make all sorts of wonderful stuff.
Wait.. You don't have a mill? Forget the sander, guy buy a knee mill!
Theres a used machinery dealer in Saint Pete, Clearwater that advertises on Craigslist, says he has Bridgeports starting at 2k
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SteveHGraham
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Re: What are Reasonable Goals for Home CNC?

Post by SteveHGraham »

I have a knee mill, but it's not CNC. It's CSC. Clueless Steve Control.
Every hard-fried egg began life sunny-side up.
redneckalbertan
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Re: What are Reasonable Goals for Home CNC?

Post by redneckalbertan »

SteveHGraham wrote:It's CSC. Clueless Steve Control.
Thanks for the chuckle!
kvom
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Re: What are Reasonable Goals for Home CNC?

Post by kvom »

If you do a lot of threading on a manual lathe consider a die head.

I've had a Novakon CNC bed mill (bit larger than a Tormach) since 2009. Accuracy is +/1 .001" on all three axes. Any part that requires arcs or angles gets done there, as well as any pocketing. I do thread milling on the CNC mill for short threads on short workpieces (e.g., studs).

Sizing stock and drilling is usually a Bridgeport job. The rotary table is gathering dust.
V8 BUG
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Re: What are Reasonable Goals for Home CNC?

Post by V8 BUG »

Home CNC can be as good if not better than pro. It really depends on who is running the machine. I have seen million dollar machines produce garbage with the wrong operator. Attached is a couple pieces I have made on a Home Mach 3 driven bench CNC mill. I'm happy with the machine, but wish it was larger.
Image
Image
BUILDING IT IS MORE FUN THAN BUYING IT
hanermo
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Re: What are Reasonable Goals for Home CNC?

Post by hanermo »

Anything is possible..
I am at the "high end" with a goal of doing perfect threads on a shop-modified cnc lathe.
I am also a pro, as I make money from it, and have sold 60+ large industrial machines.

So far, I have spent 2000 hours and 4k€ on a goal to be able to make good threads, over 8 years.
I expect to have it working well, soon.

I will be making leadscrews, and instrument stuff, to near-zero-micron error.
Most cnc retrofits, and most lathe retrofits, are not too well done by machine-shop standards, imho.

Some common problems:
1. Direct driving steppers. Not enough resolution. Not enough accuracy.

2. Index pulses. These are usually not crisp, dont trigger cleanly, and have too much variation at different RPM ranges.
In my opinion and experience, only encoder based index pulses are good enough.
We documented this decisively, using a commercial index pulse board, and proved it was not good at all.
Logging at 533 Mhz to ram, microsecond-level accuracy from 533 Mhz hardware clock.

3. Most screws are not rigid enough. Backlash may or may not be a concern.
Screw mounts are usually not good. Lean on it, watch with DTI.
My acme screws work well enough, so zero-backlash on z is not really necessary, for 99% of uses.
For blind bores, backfacing blind, counterbores inside objects, you really need zero backlash screws.
Solution: Bigger ballscrews and preloaded mounts.

4. Most hardware pulse boards (all of them) are not well documented.
Many features dont work.
Many features work wrong or differently.
None of this is documented anywhere.

5. Couplers too small (servos) or not rigid enough,
not using motion-control belts and pulleys (like HTD, GT2 M5 etc),
too small belts (M3, XL),
too small ballscrews (always !)

Some common problems with hardware boards are
speed,
homing,
probing,
threading,
css on lathes,
multiple toolholders or rear toolholder on lathe,
feed/rev issues aka inverse mode.
MPG inputs.
Support for conditional code (if .. then).
Support for multiple spindles.

Less needed:
Encoder inputs aka real DROs.
Secondary encoder input aka glass scales.
Screw mapping.


A good retrofit is potentially as good, or better, than a 100k VMC or turning center.
Speaking from extensive experience and factory training.
A good retrofit is also relatively expensive, 3-6k in bits and pieces.

Most of it is work, and every component is not too expensive in itself.
The end result can potentially deliver 1 micron resolution, and 1 micron accuracy in limited sizes.
(Its easy to make 10.000 cube to +/- 1 micron (or 2). Its really hard to make a 100.000 mm ruler. Temperature).

Note most VMCs like Haas, Leadwell, etc. == everyone quote about 2.5 micron +/- resolution and accuracy.

Resolution is not accuracy.
Good resolution is 2-10 better than expected accuracy.
Repeatability, resolution and accuracy are all different things.

Fwiw.. my step size is 0.2 - 0.3 microns, and I use servos these days.
Servos cost == the same as bigger (nema 34 size) steppers, approx 130€ per piece.
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