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Hi Izzy.

 

I am designing the machine as a stand-alone so its not reliant upon a mill or similar, which would make the control harder to work out with retro fitting etc (as you probably know). The cutter spindle bit is still being designed by myself. The intention is to build in the ability to angle the cutter upto 30 degrees which should allow the cut skew gears for worm drives (but not quite enough for bevel type gears). There is a source of gear hobs from China so I have one already (0.2Mod) to setup the machine. If it works then no doubt this can be swapped out for others.

 

Julia.

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Hi Julia,

 

You can’t really cut bevel gears with a hob, (well unless you fudge them like I would!), as the tooth form size is not a constant, getting smaller towards the centre. Didn’t know cheapish hobs were available from China. I made my own crude cutters, but this was decades ago before the web arrived. So of course I made them the size of the worm and just fed them in straight. 

 

Izzy

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Hi Izzy.

 

52 minutes ago, Izzy said:

Hi Julia,

You can’t really cut bevel gears with a hob, (well unless you fudge them like I would!),

 

I seem to get mixed messages regarding that. Some say you can and others not. My theory was to try it and see!

http://modelenginenews.altervista.org/techniques/skews.html

 

53 minutes ago, Izzy said:

Didn’t know cheapish hobs were available from China.

Izzy

 

Plenty of places around like this if you are prepared to take the risk

 

https://www.aliexpress.com/item/32508729832.html?spm=a2g0o.productlist.0.0.2d4d2a35zkQ3YP&algo_pvid=4073d1ab-5dc0-41ef-baef-5b58a7c18718&algo_expid=4073d1ab-5dc0-41ef-baef-5b58a7c18718-19&btsid=2100bb4c16031810784491686e838f&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

 

Julia.

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@missy 's projects with the Proxxon mill are seriously impressive and inspiring. But I think on balance I'm a little reluctant to take on converting mine to CNC and making other tweaks to it that seem to follow from that - at least yet. One of the things that puts me off is the fact it seems like most routes to fitting the Proxxon mill with CNC preclude also using it manually anymore? 

 

However I have been wondering about getting one of the cheap Chinese "CNC Router" machines (always described by their bed size as 3018 or whatever) to play around with CNC cutting flat materials - especially plasticard and PCB. I bought one of the cheap Chinese laser "engravers" with the idea of replacing my Silhouette cutter, but while its good for card and thin ply, it obviously can't do plastic or metal (inc. PCB). 

 

Something like this looks like it might be useful - any thoughts on what to look for? GRBL control systems ('industry standard' for hobbyists?) and an ER11 collet (i.e. named standard) sound like they should be good features?

 

https://www.ebay.co.uk/itm/CNC-3018-Pro-GRBL-Control-CNC-Router-Machine-3-Axis-Laser-Engraving-Machine-UK/224091978291?hash=item342cec3a33:g:tTgAAOSwCctfGp7s

 

Applications I'd have in mind would be milling thicker and textured plasticard for buildings, and I have the idea of trying to mill turnout bases for my experiments in smaller scales (Z and T) from single sheets of PCB, using DXFs from Templot, rather than trying to work with individual sleepers. I'm imagining something like the linked machine might work for these kind of jobs, but wouldn't have a hope of working with metals. 

 

Cheers

 

Justin

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1 hour ago, justin1985 said:

Something like this looks like it might be useful - any thoughts on what to look for? GRBL control systems ('industry standard' for hobbyists?) and an ER11 collet (i.e. named standard) sound like they should be good features?

 

The 3 pin plug looks suspect and that makes me wonder what else is. There is no mention in the linked product listing about accuracy or backlash. Similar machines demonstrated on Youtube videos milling PCB tracks seem to have problems with small details (wrong size or complete obliteration of small details). I have size issues and have suffered many broken cutters despite having what is considered a low spindle runout and backlash on my Proxxon. I am not where I would like to be with the Proxxon and similar issues are I believe were what started @-missy- off with her improvements, initially to the table to compensate for/eliminate backlash. @D869 used a larger Arduino board on his so that he could have backlash compensation. Last time we were in touch he had not finished his CNC mods to the Proxxon. He may have made further progress since or been busy with other things. If you want to make small things there are more problems because the machine accuracy against desired tolerances ratio becomes significant.

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2 hours ago, richbrummitt said:

 

The 3 pin plug looks suspect and that makes me wonder what else is. There is no mention in the linked product listing about accuracy or backlash. Similar machines demonstrated on Youtube videos milling PCB tracks seem to have problems with small details (wrong size or complete obliteration of small details). I have size issues and have suffered many broken cutters despite having what is considered a low spindle runout and backlash on my Proxxon. I am not where I would like to be with the Proxxon and similar issues are I believe were what started @-missy- off with her improvements, initially to the table to compensate for/eliminate backlash. @D869 used a larger Arduino board on his so that he could have backlash compensation. Last time we were in touch he had not finished his CNC mods to the Proxxon. He may have made further progress since or been busy with other things. If you want to make small things there are more problems because the machine accuracy against desired tolerances ratio becomes significant.

 

The X and Y axes are finished and have done plenty of good work cutting out bits for the O2.

 

@justin1985 the reason I made my own motor mounts was to allow the MF70 to be swapped quickly between manual mode and CNC. It works as intended and I can swap in about 5 minutes. For quick, simple milling jobs I prefer manual mode. Happy to share the details if you are interested. You may need another machine to make the bits though :)

 

The Z axis is a lower priority and is not done yet. I did do a mockup using an offcut of laminate flooring and bits robbed from the other axes to find out whether the NEMA 17 motors had sufficient grunt for the Z. I was not able to get the motor to miss any steps during my tests - both moving the axis quickly and slowly, short distances and long.

 

GRBL on the Uno is highly optimised and pretty much beyond any further development - the Uno is full so you need to move off the Uno is you want backlash compensation.

 

As Rich said, I used an Arduino Mega 2560. I had a CNC shield and found that I needed to switch from GRBL to Marlin firmware in order to keep the I/O pin assignments required by the CNC shield. Marlin is intended for 3d printers and is a little odd for CNC but it does the job. Alternatively there are GRBL versions for the Mega with backlash compensation but I'm not sure what hardware can be used to carry the stepper drivers if you go down this route.

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3 hours ago, richbrummitt said:

How much should I compress the springs in my anti-backlash nuts?

 

 

That's a really good question! I haven't found anything that defines exactly how much you should pre-load a backlash nut. I therefore assume its very dependant upon what type, its installation, and how its being used.

 

The way I did mine was to start with the maximum pre-load then back them off until things started to work comfortably. I found that when I set them to the maximum pre-load, the stepper motors couldn't turn the leadscrews on my machine.

 

image.png.66a18e026a34e0ae3abad50895adeabb.png

 

Julia.

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I am very confused about milling bits. I looked for information online (like this blog) but I still don't know what is the best milling bit for a job.

 

In scratch-building solid brass chassis, what milling bit should I choose? There is a need to create the voids for the axle muffs, for the driving gear, the idlers, the worm-gear, shaping the chassis.

 

I understand the difference between various lengths and diameters, and I am pretty sure I will need an end milling bit with a 3.2 mm diameter shank for the MF70.

 

I still don't know what material the bit should be made of, how many flutes, coating, what end profile, what cut variety (centre, non-centre, up-cut, down-cut, compression).

 

Very confusing for a beginner...

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I find 3-flute flat ended,  which will plunge cut the most used types.   HSS is fine for most model making tasks.     Shank diameter is likely to be the biggest limitation on what you can find for the MF70.    My machine (a modified small Seig) takes 6mm cutters in an ER11 collet.  

 

An approach to "solid brass" chassis is to make them in layers.  For example, four strips of 1/16th inch thick material gives a 1/4 inch chassis (about right if then fitted with frames outside it).  Each layer can be drilled through for the item required, but not all layers have to be drilled for every hole.  When assembled, this gives pockets for gears, etc..     It may be a simpler approach than milling what is mostly round pockets.

 

 

 

- Nigel

 

 

 

 

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What is, I think, correctly called a slot drill is the most versatile bit for what you want to do because it is an end mill capable of plunging. The difference is that a slot drill also cuts to the centre of the hole it is making. Strictly an end mill does not necessarily have this feature and some will leave a central pip if you plunge with them causing problems if you then traverse without backing off the depth (the pip holds the cutter and if it is small diameter carbide the shank will snap). Except the names have got confused and misused so there are many cutters sold as end mills that have cutting to the centre of the hole so that they are essentially a slot drill and there are drills with teeth on that cut slots. 

 

I’ve used Tungsten carbide cutters exclusively in my MF70 because of the spindle speed. 3.2mm is 1/8” or close enough for the collet to close reliably. You will probably break some, especially the smaller sizes (<2mm) and they really go so do wear decent safety goggles. 
 

Don’t get hung up on flute numbers. More flutes means you can remove material faster for the same spindle speed as long as the chips can be cleared from the workpiece. This is only relevant in a production environment. You won’t go anywhere near the theoretical feeds using the MF70. 

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1 hour ago, Valentin said:

I am very confused about milling bits.

Very confusing for a beginner...

 

Hi Valentin.

I think its one of those things that comes with experience. There are many options to choose from, here are some of the methods I use...

 

1. I now use pretty much exclusively Carbide cutters, mainly from here https://www.shop-apt.co.uk/carbide-end-mills.html

 They are cheap and cut nearly everything you will need to cut. Check the shank diameter though as its important they fit your machine. I never buy just s single cutter in any size, I normally get at least 2 just in case one breaks.

2. Most standard cutters are designed to cut upto 2x the diameter of the cutter depth, your can get 'long reach' cutters if you need to go deeper but they are obviously more fragile so you need to reduce the depth of cut and / or feed rate to suit.

2. Cutters are pretty robust too, you can tell how hard to push them by how the machine sounds, if the machine is struggling then back off the feed / depth of cut. I don't normally worry about spindle speed and feed rates, you can calculate them but I just listen to the machine, you can tell if you are working a milling cutter to hard.

3. The diameter of the cutter is normally dictated by the minimum radius and / or diameter of hole I need, I always aim for a largest cutter I can get away with as these are much more robust.. To compensate for this I always aim for a cutting depth of around 1/3 to 1/2 (at a push) the diameter of the cutter when cutting the full width of the cutter.

4. As Rich says, try to avoid cutters that don't centre cut. These days its not exclusively 2 flute cutters, many smaller 3 and 4 flute cutters can cut the full width of the cutter too. It means you can 'plunge cut' meaning treat it like a drill.

5. Practice, practice, practice!

 

Julia :)

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1 hour ago, Nigelcliffe said:

 

An approach to "solid brass" chassis is to make them in layers.  For example, four strips of 1/16th inch thick material gives a 1/4 inch chassis (about right if then fitted with frames outside it).  Each layer can be drilled through for the item required, but not all layers have to be drilled for every hole.  When assembled, this gives pockets for gears, etc..     It may be a simpler approach than milling what is mostly round pockets.

 

- Nigel

 

 Henk Oversloot has a useful article on his website illustrating this technique;

 

http://www.fs160.eu/fiNeweb/Lconstruction/V36/V36.php

 

Andy

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Thank you all for your feedback.

 

I have some practice as I purchased the machine just over an year ago, I used it mostly to learn how to use it (in process I managed to brake a couple of bits); I know what you say, Julia, about "listening" the machine.

 

Nigel, Andy, I used with some success Henk's method of layered brass chassis.

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The -now retired- toolmaker at work recommended 2 flute  cutters for milling slots.

Idea is that the cutter deflects a bit when it cuts but when it only has two flutes the other flute doesn't touch any material.

Must only be valid for shallow cuts because of the twisting of the flutes

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6 minutes ago, Jan W said:

The -now retired- toolmaker at work recommended 2 flute  cutters for milling slots.

Idea is that the cutter deflects a bit when it cuts but when it only has two flutes the other flute doesn't touch any material.

Must only be valid for shallow cuts because of the twisting of the flutes

 

Some people like to use nothing but 2 flute 'slot drills' saying they cut better.

 

J.

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10 hours ago, -missy- said:

 

Some people like to use nothing but 2 flute 'slot drills' saying they cut better.

 

J.


I wonder if this is because there can be less undercut when trying to push the amount of cut. The more cutting flutes the worse this becomes, and of course HSS cutters are more flexible so can ‘bend’ under cutting forces, being pulled ever further sideways  into the cut the bigger it is. I’ve got some long reach end mills (1/4” with 4/5/6” long flutes) where you can get interesting side profiles with anything more than a very light/facing side cut. Carbide cutters are more brittle so snap rather than flex. Of course the idea that with any end mill/slot drill you can produce an exactly sized result as per it’s nominal size is a bit of a no no. The ridgity of the machine setup also has an impact. How you approach what you want to achieve depends on what you have, adjusting the methods to suit, making allowances. 

Izzy

 

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I think the best advice is not to worry about the number of flutes and just get on with doing some milling. One day you might need to care but for now you really don't. Whether a cutter can plunge does matter, of course and it's worth buying ones that can do this.

 

Did you also know there are single flute cutters?.... and reasons why they work better for some jobs... but again, to get started with an MF70 it really doesn't matter.

 

Bigger diameter mills snap far less frequently, so use the 2mm and 3mm cutters while you are learning. Make sure you have some spares in hand when you start a job that needs 1mm. Cutter strength is related to cross section, so a 2mm is 4 times the strength of a 1mm and a 3mm is... well, figure it out :) All of 'em will snap if you try hard enough though.

 

I'd reiterate Rich's comment about safety glasses. You can't tell when a carbide cutter is about to let go. I've had one ping off just by switching on the mill - it was nowhere near cutting any metal but it had done plenty of taxing work before that. My theory is that they have a 'stress lifespan' and when you've put them through enough stress cycles they will let go regardless of what they are doing at the time. They are also bl**dy sharp, as, quite often, is the swarf that they produce.

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9 hours ago, D869 said:

Did you also know there are single flute cutters?.... and reasons why they work better for some jobs... but again, to get started with an MF70 it really doesn't matter.

 

They are very good at cutting plastic.....

 

image.png.4d3e3ca9af7d3f5ef1ed71988a55ac68.png

 

Julia :)

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Julia,

 

It is not clear from your picture if there is some protection under the plastic sheet, to protect the milling bed and the milling bit. If not, is it not necessary? I always use a scrap piece of ply but I would happily not use it as it doesn't help much when I try to align the part I want to mill.

 

Valentin

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3 minutes ago, Valentin said:

Julia,

 

It is not clear from your picture if there is some protection under the plastic sheet, to protect the milling bed and the milling bit. If not, is it not necessary? I always use a scrap piece of ply but I would happily not use it as it doesn't help much when I try to align the part I want to mill.

 

Valentin

 

Hi Valentin.

 

Yes, I always make sure I am not cutting the bed of the milling machine. I think in that picture I am using an off-cut of MDF from an old TV cabinet! As I am profiling only, the flatness is not critical. One thing I have fund is really useful when cutting thin sheet material is 3M re-positional spray mount. Its great at holding material down while cutting.

 

image.png.106802a58ac3c57176093565beb5144c.png

The adhesive can be easily dissolved using IPA when finished.

 

Julia :)

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