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Re: 3020T- DJ CNC Users thread
« Reply #40 on: June 02, 2016, 08:51:22 AM »
I did an introductory CNC course down at my local hackerspace a year ago or so...
They always said that cutting aluminium takes alot of practice. The area of successfull feedrates/plungerates settings are way narrower than when cutting wood/plastics. They weren`t afraid we`d hurt the CNC in anyway (professional grade huge machine) but it would quickly become very expensive changing out the (broken) cutting heads. They also hated the cheap cutting heads available from ebay etc.

Haven`t really been down there since then, and I`ve only used the machine with plastic and alot of help setting up the toolpaths so...


dirtyhanfri

Re: 3020T- DJ CNC Users thread
« Reply #41 on: June 03, 2016, 03:29:28 AM »
With a 3.175 mm chuck it's the only way to make larger holes.

Actually you can change the collet to a bigger or smaller one

http://www.ebay.com/itm/New-ER20-12Pcs-Spring-Collet-Set-For-CNC-Milling-Lathe-Tool-Engraving-Machine-/291676115522


I bought one of this sets and it's nice to have around, I usually keep the 3,25mm. but sometimes I'm using smaller ones for drill bits.

Working on it...

ruffrecords

Re: 3020T- DJ CNC Users thread
« Reply #42 on: June 03, 2016, 08:47:17 AM »
With a 3.175 mm chuck it's the only way to make larger holes.

Actually you can change the collet to a bigger or smaller one

http://www.ebay.com/itm/New-ER20-12Pcs-Spring-Collet-Set-For-CNC-Milling-Lathe-Tool-Engraving-Machine-/291676115522


I bought one of this sets and it's nice to have around, I usually keep the 3,25mm. but sometimes I'm using smaller ones for drill bits.

Cool. I am learning new stuff every day. I just checked my unit and the thing that screws in and holds the collet in place has a hole about 8mm in diameter so it could easily accommodate collets designed for larger sized end mills. Thanks for the tip.

Edit: I just took my collet holder and collet off. The holder has ER 11A written on it so I guess it is an ER11 type. Unfortunately the collet does not come out of the holder  - not sure what holds it it but it definitely will ot come out. I gues I am stuch with 1/8 inch shank mills.

Cheers

Ian
« Last Edit: June 03, 2016, 08:59:15 AM by ruffrecords »

gyraf

Re: 3020T- DJ CNC Users thread
« Reply #43 on: June 03, 2016, 12:05:36 PM »
ER11 collet should come out - not much sense in having a one-diameter-only collet.

E.g. http://www.banggood.com/7pcs-ER11-1-7mm-Spring-Collet-Set-Chuck-Collet-for-CNC-Milling-Lathe-Tool-p-998449.html

Jakob E.
..note to self: don't let Harman run your company..

Gold

Re: 3020T- DJ CNC Users thread
« Reply #44 on: June 03, 2016, 12:40:27 PM »
Collets are taper fit. If you give the spindle holder a couple of good whacks  it should loosen up. I usually use the collet wrench(s) used to tighten the collet nut.
« Last Edit: June 03, 2016, 12:44:42 PM by Gold »

ruffrecords

Re: 3020T- DJ CNC Users thread
« Reply #45 on: June 03, 2016, 01:41:24 PM »
ER11 collet should come out - not much sense in having a one-diameter-only collet.

E.g. http://www.banggood.com/7pcs-ER11-1-7mm-Spring-Collet-Set-Chuck-Collet-for-CNC-Milling-Lathe-Tool-p-998449.html

Jakob E.

Yes, but how? I saw something on the net about there being some sort of spring washer inside. When first inserting a collet you push and twist it but there is no instruction about how to remove it.

Cheers

Ian

ruffrecords

Re: 3020T- DJ CNC Users thread
« Reply #46 on: June 03, 2016, 01:47:51 PM »
I have done some simple cuts on wood with reasonable success. I found the spindle needs to be set to max. I love the sort of musical notes you get when doing circles.

Right now I am struggling with clamps. The screws in the ones I have were just about right for the thickness of wood I was using but now I want to try 2.5mm aluminium. I plan to clamp it on top of a scrap piece of aluminium but I cannot get the clamps to work on something this thin. Either I am doing something wrong or I need some shorter screws. attached is a pic of how they recommend doing it in the instruction manual but my screws are so long this just does not work.

Cheers

Ian

Re: 3020T- DJ CNC Users thread
« Reply #47 on: June 03, 2016, 02:31:36 PM »
We had a "sacrifice" board of a special kind of very robust mdf under the cnc. You will inevitably cut deeper than you want, and it`s uncool cutting your own cnc to pieces  8) So we just clamped whatever we were cutting by screwing them into the "sacrifice" board (with holes made with the cnc using ordinary clamps).

dirtyhanfri

Re: 3020T- DJ CNC Users thread
« Reply #48 on: June 04, 2016, 12:20:37 AM »
I found clamping the work surface quite more complicated than expected...

I use some of this:

=

I had to do some adapter plates with delrin to fit the in the T slots and they work reasonably well.

But my best solution is screwing the material directly to the slots, using a sacrifice piece under it of course.

I use bigger  pieces than needed just to have room enough to drill four M6 holes (I have some templates made on wood) and fix it to the work table using some screws and nuts. That way the work piece won't slide or move, it's attached to the machine itself, is the best way for me.
Working on it...

ruffrecords

Re: 3020T- DJ CNC Users thread
« Reply #49 on: June 04, 2016, 02:00:15 AM »
I am glad it is not jsut me who finds this hard. Thanks for the tips.

Cheers

Ian


audiomixer

Re: 3020T- DJ CNC Users thread
« Reply #50 on: June 04, 2016, 04:22:39 PM »
most of the time is spend mounting the work on my mill. then doing it a second time when the work slipped during milling.... a aluminium plate with holes in a pattern seem to work well for smaller stuff.

my ER25 collet chuck has a screw holding it in the morse taper - yours won't I guess. but if you remove the nut, then the collet is hold in the nut and can be taken out with a light sideways motion while pulling it out. the other collet (you usually have a set of increasing collets with a 1mm range per collet) needs to be put in the nut a little sideways. it then clips in and can be screwed into the chuck.

- michael

ruffrecords

Re: 3020T- DJ CNC Users thread
« Reply #51 on: June 04, 2016, 07:02:49 PM »
most of the time is spend mounting the work on my mill. then doing it a second time when the work slipped during milling.... a aluminium plate with holes in a pattern seem to work well for smaller stuff.

my ER25 collet chuck has a screw holding it in the morse taper - yours won't I guess. but if you remove the nut, then the collet is hold in the nut and can be taken out with a light sideways motion while pulling it out. the other collet (you usually have a set of increasing collets with a 1mm range per collet) needs to be put in the nut a little sideways. it then clips in and can be screwed into the chuck.

- michael

I have found that most end mills are avaialable in either a 3.175mm or 6mm shank size. I already have a 3.175mm collet so I have bought another nut and a 6mm collet which between them should do all the sizes I need.

Cheers

Ian

ruffrecords

Re: 3020T- DJ CNC Users thread
« Reply #52 on: June 05, 2016, 03:56:56 PM »
I managed to sort my clamping problems. I found some shorter M6 bolts and I could then clamp a pair of aluminium sheets securely to the bed. I then tried milling some 20mm diameter holes using a 3mm end mill in a 2.5mm aluminium sheet.. The first try used a feed rate of 100mm/min and a cut depth of 1mm. The spindle ground to a halt near the end of the first rotation. I then halved the feed rate and halved the cut depth. This worked but the edges of the hole have bad burrs. Lastly  I halved the cut depth again and added an extra step to break through into the sacrificial plate below. Again this worked but again there were bad burrs

I am not sure what is causing this but perhaps the aluminium is soft?

In the attached pic the three holes are marked 1,2 and 3.

Cheers

Ian

Gold

Re: 3020T- DJ CNC Users thread
« Reply #53 on: June 05, 2016, 09:14:08 PM »
For aluminum a two flute end mill works better than a three or four flute end mill. It clears the swarf better. Usually if you order an end mill for aluminum it is a two flute model.  Not sure what you are using.

Landins

Re: 3020T- DJ CNC Users thread
« Reply #54 on: June 06, 2016, 05:01:16 AM »
Did you mist with sprituosa of any kind? It will improve performance. I found that light passes, 0.5 mm, not so slow works fine. Risk for clogging if going too slow.

ruffrecords

Re: 3020T- DJ CNC Users thread
« Reply #55 on: June 06, 2016, 01:43:07 PM »
Did you mist with sprituosa of any kind? It will improve performance. I found that light passes, 0.5 mm, not so slow works fine. Risk for clogging if going too slow.

Now that is interesting. This whole question of feed rate and cutting depth is very confusing. I have a great book called CNC Machining in the Workshop by Dr. Marcus Bowman and he includes formulae connecting cutting speed, drill diameter,, spindle speed and feed rate. Can you expalin why a slow feed rate risks clogging?

Also I cannot find a reference to sprituosa? What is this?

Cheers

Ian

Gus

Re: 3020T- DJ CNC Users thread
« Reply #56 on: June 06, 2016, 05:50:36 PM »
Some panels do not machine well even with a two flute and a mist system on a Bridgeport.  I think some panels are a mystery alloy

I find water jet cutting works better.  I follow up with a reamers to get the right size for smaller holes.  I ask for the holes to be cut a little smaller

Gold

Re: 3020T- DJ CNC Users thread
« Reply #57 on: June 06, 2016, 08:00:26 PM »
I just have a manual micro mill. I've found tapping wax to be the easiest, least messy, work best combination. I have no experience with automated lubrication/flush systems.  I also keep a chip brush handy and use it often.   

audiomixer

Re: 3020T- DJ CNC Users thread
« Reply #58 on: June 06, 2016, 08:14:01 PM »
when doing holes in aluminium you might have to take  a two pass approach: pierce the material, maybe with a drill first (tool change) and then run along the outer diameter. circular tool path or nautilii tool path (more advanced cam software can generate quite complex tool path) can yield much better results.

you approach has the disadvantage of climb and conventional cut at the same time. one side is climb milled, the other conv. milled. this is something inherent when you first pierce your material.

tool speed (feed, rpm, depth of cut is sometimes a mistery for me too. you have to get a feeling for the chips you make and sometimes it is better to go for a bigger cut. I think this is because you get more cutting and less rubbing. chips are cut and deformed at the same time. aluminium tens to go soft and clog up your sharp edged tool quite easily if munched half hearted.

did you add some board underneath your workpiece? it's good practivce not to cut into your table (note to myself - print last sentence and take to workshop...)

last but not least: spiritus seems to be a suitable coolant / lubricant for aluminium. just bought a bottle, will test it out. cuttin oil or any mineral oil will do the same for steel, but has less effect on aluminium.

cheers,


michael

ruffrecords

Re: 3020T- DJ CNC Users thread
« Reply #59 on: June 07, 2016, 02:17:14 AM »
Thanks for the tips. Last night I tried the same cuts on a proper anodised aluminium front panel. I tried it with and without lubricant (cutting oil). The cut with lubricant was definitely better than without but in both cases there was a lot less burring so the grade of aluminium seems to be an important factor. I then did another lubricated cut in the original aluminium sheet I first experimented with and this gave a much improved cut also. I have read that water based coolants are better for aluminium. I will try to find some spiritus locally.

Cheers

Ian

Edit: It looks like spiritus is also known as denatured alcohol.

Ian
« Last Edit: June 07, 2016, 05:49:58 AM by ruffrecords »