Author Topic: hot chips (at last)  (Read 9040 times)

Offline russ57

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hot chips (at last)
« on: November 24, 2011, 10:04:50 PM »
So, I've finally got my new mill installed, (not so easy cos its at the bottom of the garden, literally!) and its vfd is functional. I still need to build a proper control panel, but i thought i needed to at least make chips!
since  :worthless:
the easy bit of the path...

the next bit...

The toptech DM15, a 6x26 style baby knee, in place...(table not yet replaced)

and (eventually) first result...



Now, some questions.. :nrocks:.
1. The mill is three-phase, powered by a 'powtran' VFD.  Can anyone offer an opinion on the following questions...
What is a reasonable minimum frequency?
What is a reasonable maximum frequency?
These two questions will obviously determine what belt ratio I would use as standard, and if i would need to change it routinely.

2. I discovered that hot chips are hot, :borg: having one insert itself into my collar. I am sure the scar will heal....Apparently my beard isn't long enough to catch them, and i know growing it longer is not a domestically-acceptable option. Does anyone have any recommendations for appropriate clothing to avoid this?

3. The mill has an R8 taper. When i first inserted the facemill, there was clearly a key of some sort in the spindle. By the time i got to the end of the second face of this bit of angle, there clearly wasn't, announced by significant slippage...
Some quick googlesearch revealed that as many people remove the 'key' (typically a set screw?) as take pains to ensure it is intact.  However, I clearly didn't do the drawbar up tight enough. How tight should it be? The supplied bar is effectively a long bolt, with a threaded 'collar' which seats on top of the spindle. The collar can't be tightened when it is sitting on the spindle (recessed too deep).

4. Next task is to build a control 'pendant' for the VFD. I am planning on  a large 'stop/start' button, smaller forward/reverse, forward jog, reverse jog, and speed pot, with a digital frequency meter driven from a 60-slot disk on the top of the spindle.  I could fit this in place of the original mill controls under the table, or possibly higher up at the side of the column. Any comments on this plan?

5. I am starting to regret not springing for the powerfeed option (although that one didn't have 3phase), and will probably build one. Is it good/bad/otherwise to include controls for that on the main mill control panel?

regards,

russell
(theoldwindmill.net)
« Last Edit: November 25, 2011, 12:29:03 AM by russ57 »

Offline hopefuldave

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Re: hot chips (at last)
« Reply #1 on: November 27, 2011, 09:04:44 AM »
Hi Russ, you seem to have the right trade-off - bigger shed than mine Vs worse access!

Re the min/max frequency, bear in mind there are two issues to bother you - at the low end there may be insufficient airflow to keep the motor cool over long periods, but frequencies can go down to 10-15Hz. The torque delivered will be the same as at a medium frequency, but as power = torque x RPM, you *will* get a drop in actual power. This makes it worth swapping pulleys even if you have a VFD! I take my lathe VFD down to 5Hz for "inching and jog", but have an auxillary motor cooling fan that the VFD switches on when it drops below 33Hz...
At the high frequency end, it's bearings, belts and pulley-balance you have to think about, I've found I can take mine up to 75Hz without any problems, but not for long as my lathe spindle has plain bearings rated at 1500RPM and that can take it to 2250...

Hot chips... ahh, yes. I wear a baseball cap backwards (to keep 'em from the back of my neck) and I have a deflector shield made form a piece of clear ABS plastic fitted with a hard-disk magnet that I stick in the way of the chips :)

Re the drawbar, I'd guess spanner-tight (i.e. not *swinging* on a spanner the right length for the bolt head)? R8 tapers aren't as "self-locking" as Morse, hence the pin, but I'm always a bit reluctant to hammer hard on the end of *any* drawbar in attempt to release it - I often put a hefty block against the spindle first, to try to preserve the bearings, dunno if it helps? I have had some intractable stuck tapers over the years, sometimes it needs a pair of wedge collars to get a chuck out :(

Control locations are a personal thing, I'd say use it for long enough to get annoyed at what's in the wrong place, and work from there! Whatever you do, be sure you have EStops all over the place - with a VFD you should be able to make it a braked stop (e.g. DC braking) which will be way faster than just cutting the power and letting it coast. Add a relay or similar to cut the power feed (if you fit one), too - otherwise you'll be sure to stop the spindle but not the feed, and watch that brand-new solid carbide form cutter that cost the week's beer money go spinning away in dozens of pieces - DAMHIK,OK?

Stick an Emergency Power Off switch somewhere convenient - by the entry door's good, that way SWMBO can turn the machine off without being beaten by your corpse as it flails around with the spindle... ;)

Dave H.
Rules are for the obedience of fools, and the guidance of wise men.

Offline russ57

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Re: hot chips (at last)
« Reply #2 on: December 01, 2011, 03:40:02 AM »
thanks for your words dave.
unfortunately, my shed isnt very big...10' by 17'. Anyway, its bigger than some, and it exists. I will take some more shots and put a thread in 'my shop'.  i would like better access though - just cant see anyway to get a heavy lathe down, for example.  On the other hand, theres no room for a bigger lathe. Must evict some junk...


i find i have a slight character 'flaw' - i only like doing things once, so i spend forever planning it so it is 'perfect' - to the point 'it' often never gets done at all! I  must learn the difference between what i can redo and what i cant...

i will fix up a chip shield - they went everywhere. i'm in the process of laying  a salvaged interlocking veneer type floor. should make it easier to sweep at least, but better if the chips aren't where they aren't supposed to be.

the 'shed' has a main switch inside the door, i turn off all power whenever i leave, so that will probably serve as emergency power.  I had intended to use the mill's built-in NVR switch as master power off for the 3phase control, but with the motor not running it doesnt draw enough power to hold the relay in. 



Offline Bernd

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Re: hot chips (at last)
« Reply #3 on: December 01, 2011, 09:32:56 AM »
- just cant see anyway to get a heavy lathe down, for example.  On the other hand, theres no room for a bigger lathe. Must evict some junk...

Russ,

After you've evicted some junk to get a lathe into your shop you may want to see how I moved something heavy down hill. I did have some help from a 4 wheeled vehicle though.  :) It may give you some ideas.

http://madmodder.net/index.php?topic=381.msg1413#msg1413

Bernd
You can't fix "STUPID".

Offline Xldevil

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Re: hot chips (at last)
« Reply #4 on: December 01, 2011, 01:18:47 PM »
Hello,Russel.
Looks like my milling machine is virtually the same as yours ,besides the fact that mine has a MT3 spindle.
This milling machines are more or less clones of the Clausing 8520/8530 mill.


I tapped the upper part of the Spindle M14x1 and screw cut the the top of the drawbar as well.
At the bottom end the bar has a M12 x  1,75 thread.
Because of the different pitches, I've got a self ejecting drawbar.
No hammering anymore.

(picture from http://dampfundmehr.de/)







Upper section of the drawbar screw cut M14x1


Tapped the inside M14x1


(picture from http://dampfundmehr.de/)

I can recommend the
http://finance.groups.yahoo.com/group/6x26millingmachines/
community
which will give you a lot of useful informations.

I recently installed a power feed to the x-axis and I'm pretty happy with it.
I got it from Axminster for a reasonable price and very fast.



My 3 phase motor is controlled by a digital inverter.I can really recommend that.


Cheers,Ralph

Offline russ57

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Re: hot chips (at last)
« Reply #5 on: December 04, 2011, 08:49:45 PM »
thanks.
Ralph, since i'm a raw  beginner, i think it will be a while before i have enough courage to dismantle the spindle to be able to tap it...but it is a great idea.
Bernd, i read your post and everything else i could find on moving heavy stuff. Every circumstance is different, but i realised my problem wasn't so bad. Of course, getting it in (down) is one thing, up and out is another altogether - somewhere recently i read of a bargain mill purchase, buyer to remove from basement...
I like the vfd, starting up it sounds as though it is slipping or hunting, but quickly stabilises. I have ordered a freqency meter which should make it more obvious what is happening.

and yes, i am a member of yahoo 6x26.

regards

russell