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CNC dedicated mill or CNC converted mill?

Which path to follow.

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Andrew Evans14/07/2020 09:32:45
321 forum posts
8 photos

Is it a possibility to 'rough out' with a hobby CNC mill and then finish the crucial dimensions with say a surface grinder or in a manual way? Based on what others are saying it sounds like producing parts to that spec purely with a CNC mill might be beyond your budget

Edited By Andrew Evans on 14/07/2020 09:41:12

Baz14/07/2020 10:24:30
409 forum posts

Why don’t you sub contract the work out to those with the 1/4 million pound machines and the small fortunes worth of tooling not forgetting the temperature controlled environment who can actually do the job, save you an awful lot of s**t, grief and aggravation.

John Pace14/07/2020 12:46:57
191 forum posts
180 photos

Posted by Andrew Johnston 13/07/2020 22:13:49

Quite so, but even measuring a cutter diameter is non-trivial. In theory
an even number of flutes can be measured with a standard micrometer.
But it's not easy to determine if the flutes being measured are precisely
in line with the measurement axis. An odd number of flutes is more
of a problem. Of course one can buy flute micrometers for 3
and 5-flute cutters. A quick search found a Mitutoyo 3-flute
micrometer on sale at the bargain price of £224, plus VAT of course!


Hi Andrew

I use much simpler methods for doing this as seen here in the photo.
With the cutter mounted in a vee block the relative height of the shank
and the highest point of any cutting edge enables the cutter diameter
to be calculated.

3 flute cutter.jpg


I would normally do this at the time the cutter is sharpened as the
cutter can be rotated on the machine about its center and measured in
this way , if a specific size is required since the diameter is known it
is a simple matter to regrind to the required size.

The real fun starts if a tapered cutter is ground since there is no reference
diameter, a small test piece is cut to work out the relative center distance
at the full cutter depth.This pair of 6 mm cutters were reground at approx
3 deg taper and 1 mm radius edge to cut the vanes on this turbine
compressor wheel.

John

Tapered cutters

Compressor wheel


Barrie Lever14/07/2020 12:49:14
653 forum posts
75 photos
Posted by Baz on 14/07/2020 10:24:30:

Why don’t you sub contract the work out to those with the 1/4 million pound machines and the small fortunes worth of tooling not forgetting the temperature controlled environment who can actually do the job, save you an awful lot of s**t, grief and aggravation.

No guarantee that they will do the job for any reasonable rate and might be more agro than doing it yourself.

What the OP really needs is a prototyping setup like these guys produce

**LINK**

The trouble is it is about 10 times the stated budget, so what Duff has to do is to try and see through the lines of the MDA offering and specify something that does the same without compromising his final goals.

Regarding cutter diameters, I don't measure them at all, I enter the diameter into CAD and home in on the final finished dimension with a waypoint for measuring, at this point I can measure the total system error (backlash, machine flex, tool flex etc) and make a final correction in CAD. I always climb mill so always have a bigger part if no corrections are made.

This could also be done by fudging the G41/42 figures.

B.

Edited By Barrie Lever on 14/07/2020 12:59:40

JasonB14/07/2020 13:10:36
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If error were the same in X&Y it would be easy enough to do it with the CAM too, just entering a larger or smaller cutter dia eg if your test was coming out 0.02mm too large with a nominal 6mm cutter you could just enter cutter dia as 5.98mm and the path would then run 0.01mm closer and remove the oversize.

Barrie Lever14/07/2020 13:43:01
653 forum posts
75 photos

Jason

That is the way that I do it, of course the problem comes if the error is significantly different in X and Y, I have always managed to find a happy medium between the X,Y errors though.

I am not that familiar with G41 and could not always accommodate the run in whilst it corrects the tool diameter.

I don't like people blindly relying on CAM though, a working knowledge of G codes is very worthwhile to learn.

B.

geoff adams14/07/2020 14:50:57
177 forum posts
196 photos

Barrie

g41 g42 are cutter comp on dia of the cutter program the profile of your part in cam or by hand enter the cutter dia in the machine control if part comes out oversize alter the dia on the machine not in the cam

back in the day with no cam this was very powerful tool to hold tight tolerances on profiles.

i have mach 3 on two of my mills and is not always happy with these g codes fusion 360 has an option to use g41 g42 that i do use

back to the original thread on holding tolerances on cnc machines we had a job that was about 3" 3" steel gear plate the tolerances were.0005 on pitch of holes we did this on a big Matchmaker bed mill had to warm mill up for about 3 hours run job 3 hours what was happening as the machine warmed up the colum moved stable for about 3 hours then moved again to hold these tolerances everything needs to be temp controlled room including inspection all our jig borers were in temp controlled rooms this was in the aerospace industry

Geoff

Barrie Lever14/07/2020 15:39:58
653 forum posts
75 photos

Geoff

Some machines don't have G41/42 so it has to be done in CAM, one of my machines does and one does not.

0.0005" so half a thou, surprised you had to go to that trouble for half a thou across 3 inches, when I was in aerospace we had a Matchmaker that was used by Noah when he loaded the arc, code was feed in on a punched tape, it was only used for one job, jig borers were out in the open workshop.

I have never seen this elusive temperature controlled machine room !! Seen plenty of NADCAP composite clean rooms temp. controlled though.

B.

geoff adams14/07/2020 16:47:16
177 forum posts
196 photos

Barrie

back in my day we did not have cam or a computer everything done with calculator and log tables never came across a cnc machine that did not have g41 g42 must b be a nightmare without cam

no i have never seen a temp controller machine shop point being if you do need to hold these tols.these need to be considered if the tolerances are are needed or is a draughtsman being over the top for example job on 4 axis one hole +- .002 on pos and on dia on assembley turns out to be a hole for a screwdrive ??

Barrie Lever14/07/2020 17:13:00
653 forum posts
75 photos

Geoff

Meet plenty of design guys particularly in aerospace who specify tolerances that are way too tight, patterns that are 4 metres long with plus minus 0.2mm.

I have sat down in design review meetings and really told these type to wake up and smell the roses.

We are speaking the same language.

B.

geoff adams14/07/2020 18:03:17
177 forum posts
196 photos

Barrie

many a time i have sat with a cnc mill doing nothing costing i dont no what and production getting behind while QA drawing office and planning argue what is practical in the real world looked good on paper is the tolerance needed can it be achieved +- 002 from cast faces ok today you can probe it not in my day got fed up with all the crap and moved to Christchurch Dorset and went into building trade now retired

back into engineering love it iam my own boss QA up to me

Geoff

Duff Machinist14/07/2020 18:57:59
12 forum posts
Posted by Emgee on 13/07/2020 23:04:13:

Anyone had a Malware TROJAN Warning when using the Sieg CNC Catalogue thingy link an earlier reply ?

Emgee

Edited By Emgee on 13/07/2020 23:05:23

Odd. I have the same Malwarebytes Premium (full), and it didn't crop up when I clicked on the website.

Duff Machinist14/07/2020 19:18:38
12 forum posts
Posted by JasonB on 14/07/2020 07:16:41:

One other thing to consider ... ...and the type of cut it is taking.

Edited By JasonB on 14/07/2020 07:38:07

Thanks Jason. Absolutely.

Way back when I was young and beautiful, I had access to a Golmatic miller with DRO (£12k worth 20 years ago). The friend who owned it allowed me access to the machine on a regular basis. I was able to cut my teeth on it and spent a lot of time practising on scrap metal to get to know the machine, set-ups, etc. Unfortunately, the owner died 10 years ago and my milling days were abruptly ended (I couldn't afford the machine when it was put up for sale).

Some of my 'hobby' projects back then included some complex cutting and I dearly wished for a CNC but back then, as you know, CNC was not as accurate as a manual machine (and still isn't, but to a lesser degree nowadays).

I therefore have the basic milling skills and understanding that thing are far from simple. I'm going into CNC eyes wide open and not expecting simple (or cheap) solutions

Thanks for the youtube link, I'll have a look. I've gone off gantry machines, but it's all good education regardless. face 1

Duff.

Duff Machinist14/07/2020 19:25:57
12 forum posts
Posted by Neil Lickfold on 14/07/2020 08:45:49:

Making parts consistently to 10um is actually a tall order. Barrie is far from a beginner machinist and buying a machine and replicating what he has done is not an easy achievement. A Fanuc robodrill come to mind. **LINK** or the small Hass mills etc. But these are well over the hobby budget but are the lower end of dedicated mills. What you really want is a second hand DMG that is 10 years old or so. Is another option.

There are many others. Some of the machines I saw a few years ago were not capable of making parts to 0.01mm .

You will need to invest in good cutters and good holders. Currently the better ones are the holders that seat on the taper and the face of the spindle. The new series of hydraulic collets are actually out performing the shrink collet chucks.

Agree. I don't know Barrie, but he comes over as someone who knows his stuff and is good at what he does (thanks Barrie!). teeth 2 I'm expecting a learning curve.

I did look at DMG a little while ago, and checked for machines (and others) on the European trade sites. All the ones I could find (used) were too large and way too expensive. Quality holds its price (to a degree) I guess.

I should also have said that the CNC mill would have to be benchtop size, although maybe my weight requirement of around 150-500 kg might have hinted at that.

I'll have a look at the Fanuc and see if specs are within range. Thanks Neil.

Duff.

Duff Machinist14/07/2020 20:10:24
12 forum posts

Oops, sorry everyone. Hadn't realised there was another page of replies. I'll try and reply to all in one post.

Posted by Andrew Evans on 14/07/2020 09:32:45:

Is it a possibility to 'rough out' with a hobby CNC mill and then finish the crucial dimensions with say a surface grinder or in a manual way? Based on what others are saying it sounds like producing parts to that spec purely with a CNC mill might be beyond your budget

Edited By Andrew Evans on 14/07/2020 09:41:12

Thanks Andrew.

Yes, I could rough out but I would need to make jigs, etc., and if I'm at that stage I would be in a position to finish the part off while still in the jig. In fact, all the work could be finished on a manual machine with DRO (as nearly all jobs can be), but it would be a really painful and long process. Having said that, I may have to go that route anyway.

Posted by Baz on 14/07/2020 10:24:30:

Why don’t you sub contract the work out to those with the 1/4 million pound machines and the small fortunes worth of tooling not forgetting the temperature controlled environment who can actually do the job, save you an awful lot of s**t, grief and aggravation.

Baz - comes down to cost. There would be several parts that would need to go out. On top of that, I'm always worried that they won't do the job properly. I have rarely been satisfied with (non-machinery but nonetheless skilled) work delegated to someone else - they invariably screw up. Also, if I've made a mistake in my CAD file (cos' Sod's law), it'll cost me double. So yes... I'd feel really iffy about that but understand where you're coming from. High spec' mill ownership is not cheap.

I would still need a mill of sorts so I'm not sure if I'll be saving any money anyway.

Posted by Barrie Lever on 14/07/2020 12:49:14:

No guarantee that they will do the job for any reasonable rate and might be more agro than doing it yourself.

What the OP really needs is a prototyping setup like these guys produce

**LINK**

...

B.

Edited By Barrie Lever on 14/07/2020 12:59:40

Thanks Barrie,

Yes, no guarantee, and no guarantee that I've got the part right as these would be prototypes and prone to amendment. As a consequence, cost inreases.

Thanks for the link. Hadn't looked at MDA and those are the machines that would fit the bill perfectly. The Q350 looks spot on. While it appears it's their 'entry level' (their Wabeco aside), no price is given but I'm guessing 15-20k. The other machines have as good or better specs but, of course, are appropriately priced.

Interesting that they're synthetic granite (hmm, now there's a thought cool... ..I wonder if I could ma...)

So far, the Wabeco range seems to be the best for the price. Yes, I would definitely be happy with a MDA machine but I'd need a wind fall. I'm discounting the Chinese mills as they seem to need refinishing to get any high accuracy result out of them, and to be honest, they're not far off the price of Euro/US made machines, after all is said and fixed.

It may be that I'll have to make do with a manual Wabeco (or similar) and DRO fitted to do most of the work, converting to CNC as funds allow (although cost of the DRO puts the machine up in the CNC range). As said in an earlier post, all the work could be done on a manual mill but the agro involved in setting up might make me chuck the whole project in. I'll have a further think on this and look at what machining steps are practicable on an accurate manual mill with DRO to get what I need. If memory serves me, I (obviously) went through this assessment only to find myself saying "I need a CNC...".

(The CNC would also make more sense if or when I went into small production mode, but that's way off in the future.)

Thanks again everyone.

Cheers,

Duff

PS. The CAD/CAM side of things is okay. While I have very little expereince of practical application, I've been able to play with a few programmes. Very daunting at first but I'm getting my head around this aspect. thumbs up

JasonB14/07/2020 20:48:58
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Posted by Duff Machinist on 14/07/2020 20:10:24:

I'm discounting the Chinese mills as they seem to need refinishing to get any high accuracy result out of them, and to be honest, they're not far off the price of Euro/US made machines, after all is said and fixed.

Have a look at what mine produced while still sat on the pallet and no cutter compensation, part I cut at the weekend had similar 0.01 deviation from drawn which is your 10microns. None of my 4 far eastern machines has been "refinished" or stripped and rebuilt.

(although cost of the DRO puts the machine up in the CNC range).

DRO would only add £3-400

Duff Machinist14/07/2020 21:42:21
12 forum posts
Posted by JasonB on 14/07/2020 20:48:58:
Posted by Duff Machinist on 14/07/2020 20:10:24:

I'm discounting the Chinese mills as they seem to need refinishing to get any high accuracy result out of them, and to be honest, they're not far off the price of Euro/US made machines, after all is said and fixed.

Have a look at what mine produced while still sat on the pallet and no cutter compensation, part I cut at the weekend had similar 0.01 deviation from drawn which is your 10microns. None of my 4 far eastern machines has been "refinished" or stripped and rebuilt.

(although cost of the DRO puts the machine up in the CNC range).

DRO would only add £3-400

Well, that's me stood corrected!

Thanks Jason.

Duff.

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