[kensbey]

Hey all,

I have taken the plunge and bought myself a mill. It is a Hare Forbes HM46 Mill, which is pretty identical to the RF45 style mills.



My Plans are as follows:

• Diy Stand with Drip Tray & coolant
• 3 axis cnc conversion with stepper motors and Mach 3
• Pnumatic Drawbar
• Maybe TTS and ATC
• Win at everything forever

The Shed I am putting it in has a low ceiling, so i will have to build my own stand to allow full movement in the z axis.

More details soon

kensbey

[kensbey]

As mentioned above, i need a DIY stand to fit the mill in my shed, and i would also like a full size drip tray to catch swarf and coolant. Eventually i will be enclosing the whole mill once it is fully CNC.

So i bought 4 x 4m lengths of 40x40mm RHS, and touched up my welding skills. I haven't done any welding since highschool, so i took a couple of practice welds on scrap to get a decent end product. Used a drop saw with grinding discs to cut steel to length. Still had to touch up some welds with the angle grinder although. i guess my welding skills are a little rusty.



Added a few coats of paint.



finished stand with Mill. The stand is quite low, because the roof at this point is not very high. my plan is to suspend a drip tray under the stand to catch swarf etc. Will also have to incorporate a filter to reuse coolant.

[LUCKY13]

You could do like my buddy did, he built a two foot wall around for the little building to set on. This gave him much more head room & storage which was what he was using the building for. The two foot wall he just build out of 2 x 4's just like you was building a wall in a house, only shorter. Then when the building was bolted down to it it was two foot taller.


Good luck with your mil and keep us posted.




Jess

[kensbey]

So perhaps the key question is: Steppers or Servos?

I'm a little bit limited here in Australia, because its a good couple of hundred dollars to get all the stuff shipped out.

Keling have good kits for both servos and steppers, and there is also a local company Ocean Controls that have good stepper kits, but significantly more expensive than Keling. Most XX-45 type conversions tend to use 70-130 kgcm (1100-1800 oz-in) per axis. (or the equivalent through timing belts).

At this stage i'm leaning towards 1200 oz-in steppers directly coupled onto the ballscrews. I think im going to get the screws from linearmotionbearings2008, which seems to be common on the forums.

any and all advice welcome

kensbey

[kensbey]

Way covers were something that i wanted to get in place ASAP. This means less cleaning of the ways and screws now, and will protect ballscrews when i get them.

I had a look at the various techniques people have used to build their own covers, but also asked around some local machine stores. I found a shop selling universal covers for 30 dollars each, and decided it wasn't worth DIY for that price. They are a folded rubber cover, with little metal strips on each end.



i was going to drill and tap holes in the table and base to mount the covers, but then i had bit of a brilliant idea (if i say so myself). i bought some neodymium magnets off ebay ($10 for 20 inc shipping). i put a couple along each mounting point and slapped the way covers straight on.



It worked much better than expected! these little magnets are very strong! I have to pull the cover sideways and slide them off the magnets to remove. i bought 1 cover for the front y-axis and two for the rear. I joined the two rear ones together and attached to the z axis and back of the table.



overall, I am very happy with the result. the covers dont move at all when the mill is in use and can be removed in 5 seconds for access to ways and screws.

[mrcodewiz]

I don't think I have seen any direct drive stepper conversions on these - only belt/reduction setups. Do you think it will work alright?

[kensbey]

i think it will work ok. I do know that some of the big haas machining centres use steppers, have seen them personally. i saw a rf-45 on youtube with steppers:

[ame=http://www.youtube.com/watch?v=alyuZv7nIpc]Rong Fu type RF-45 CNC Mill Conversion - YouTube[/ame]

i know servos are the popular route, but i can't help thinking there is going to be play in a belt driven system.

The servo route also relies on good tuning of the PID controller driving it. i know from my engineering degree that tuning a control system relies on the operating device to perform the same every operation. I have wondered if the constantly varying system dynamics present in a milling machine (switching from climb to conventional milling,3d profiling, etc) would affect the accuracy of the PID controller.

This being said, plenty of people on this forum have had great success with servos, and i'm yet to finish my conversion, so i probably can't talk. always open to hear other's opinions!

[SCzEngrgGroup]

"i can't help thinking there is going to be play in a belt driven system" - Not if properly designed, using appropriate components. They are used on all kinds of high precision equipment.

"I have wondered if the constantly varying system dynamics present in a milling machine (switching from climb to conventional milling,3d profiling, etc) would affect the accuracy of the PID controller" - At the level of performance achievable on these machines, PID tuning is not a big deal. Anyone can do it if they simply take a little time to understand what they're doing.

On benchtop machines, the choice between steppers and servos is more a matter of personal choice than anything else. The exact same level of performance can be achieved with either, with the same high level of reliability, if the system is properly designed. But take a bunch of random parts, slap them together hap-hazardly, and either is just as likely to result in a system that performs poorly.

Regards,
Ray L.

[mrcodewiz]

I may just try that route and see what happens. Sounded like he said 2800 oz on the Z. Pretty hefty. I have a couple 1200s for the X/Y so its worth a shot anyway.

[kensbey]

im going either 1200s or 1700s on all three (depending on cash avaliability when i get to that part). he only uses a 2800 on z to counter the weight of the head i think, i am planning on using gas struts or a counterweight system to do that.

The next step for me is picking some ballscrews. Im pretty set on getting some from lmb2008, as they seem the best price and a popular option too. thinking 20mm screws will be best.

do i need double ball nuts? i have seen conversions with and without, but not alot of talk about how much improvement is gained from 2. Double nuts would definitely be tight in the y, but i can always mod the base to compensate.

can anyone just using single nuts let me know if it's sufficient? backlash etc.

thanks

[Mad Welder]

........do i need double ball nuts? i have seen conversions with and without, but not alot of talk about how much improvement is gained from 2. Double nuts would definitely be tight in the y, but i can always mod the base to compensate.

can anyone just using single nuts let me know if it's sufficient? backlash etc.

thanks

Hi there just came across this thread and I've got the baby of your machine….. mine is the Optimum BF20…. and if I had the space I would add double spring loaded ballnuts simply for my own future machine requirements….but so far I have been able to get by with Mach’s backlash compensator ...and it's really up to you as to your required finished machined tolerances as to whether to fit two preloaded (spring loaded) double Ballnuts or just one Ballnut… the two spring loaded Ballnut configuration ‘will’ minimise backlash ‘more’ than the one Ballnut configuration, but with one Ballnut configuration and with the Ballnut packed with oversized steel balls and using two angular contact ball bearings on the motor end of the Ballscrew on either side of the bearing block this 'will' also minimise backlash, but as I said the necessity will be dictated by your finished machined tolerance requirements…

I'm looking forward to the build pics so post plenty of photos and the more the better.

[kensbey]

Thanks for the info!

….but so far I have been able to get by with Mach’s backlash compensator

How much error does this induce? does it significantly affect your ability to take cuts? i would like to be able to climb mill if neccessary, as it can give superior surface finish. is the small amount of backlash present in a single nut setup significant enought to affect these sorts of cuts? Any other issues with just using mach3 compensation?

[kensbey]

So with a big thanks to taark, i have now aquired some steppers, drivers and power supplies. All are from longs motors. I spent the weekend mounting and wiring all the electronics into an enclosure:



Still need to get a 3rd power supply for the z axis, but this can wait untill after x an y are running. Each power supply has its own breaker, for redundancy. the three relays are dc driven and switch the three GPO's on the side of the enclosure:



As per labels, one is for spindle, one for coolant and a spare. the spare may end up being a power drawbar at some point.

There is also a nice big emergency stop button on the side, which cuts power to everything. This is really a secondary precaution, as in most cases the mach 3 e-stop functionality should be ok. I just wanted to have a hardware wired safety cut just in case.

After a day of wiring, it was nice to see some pulses coming out of the breakout board.



Shortly after, i plugged a stepper in and got some movement! progress! heres a snap of the motor size compared to the mill:



The motors are very smooth at speed, which is nice to see. Although, when microstepping at slow speed, i still get a small noise and vibration as the rotor passes each 1.8degree step. is this normal? it is very smooth between the steps, but each step is audible.

[Robin Hewitt]

can anyone just using single nuts let me know if it's sufficient? backlash etc.

That really depends on what you are trying to achieve, a single, cheap ball nut is good for a couple of thou backlash. If that's too much you can throw lots of money time and effort at the problem, but all you can gain is a couple of thou. Maybe.

A shimmed double nut is good for just under a thou backlash after it has bedded in, maybe half a thou when new.

If you preload your ballnuts and screws with springs you can get backlash down to a point where you cannot measure it. I have about 500 lbs of preload.

Is it worth the time and money? Only if your machine is rigid enough not to bend under the tool loading. Bolt a dial test indicator to the bed, run it up against the tool tip then lean on the chuck and see what happens.

[Mad Welder]

If you preload your ballnuts and screws with springs you can get backlash down to a point where you cannot measure it. I have about 500 lbs of preload..

If kensbey wouldn't mind you posting a photo here in his thread that is if you have one, I'd sure like to see your double Ballnut setup myself too for future build modifications....

Is it worth the time and money? Only if your machine is rigid enough not to bend under the tool loading. Bolt a dial test indicator to the bed, run it up against the tool tip then lean on the chuck and see what happens.

Thanks for the tip I hadn't come across that one yet

.........is the small amount of backlash present in a single nut setup significant enough to affect these sorts of cuts?

The answer is yes when carrying out a simple circular pocket you can measure the machines diameter to the actual finished cut X,Y diameter and diagonal diameter measurements and this would give you an idea of your machines backlash error however it’s stated that to get a fully accurate backlash error measurement you should measure over a longer distance i.e. half axis movement or more if possible……

.........Any other issues with just using mach3 compensation?

Mach’s Backlash compensation error setup is fairly easy to enter data into (select the Config TAB within Mach and scroll down the dropdown menu to Backlash), however as Robin Hewitt said that you can almost eliminate or reduce dramatically backlash mechanically this would be a better approach I think as it’s always better to have as near as perfect a mechanical setup rather than relying on software to compensate….. Mach isn’t bullet proof and has given some people headaches to solve finicky issues…..but with that said Mach is also an excellent CNC software controller and I’ve had no issues yet….. well ok……apart from trying to learn the software…..

[Robin Hewitt]

If kensbey wouldn't mind you posting a photo here in his thread that is if you have one, I'd sure like to see your double Ballnut setup myself too for future build modifications....

It was a retrofit. I removed the shims from the double nuts then sprung the nuts together with a couple of Belleville washers.

I added metal collars which I turned down to get 1mm crush on the washers when bolted up tight. That gave me 500 lbf.

I admit I was getting a bit anal about backlash at this point, but this actually made it go away so I could move on. It's self adjusting, since 2009 all I've had to do is add oil

[691175002]

Software backlash compensation sounds better than it works. I am running software comp on my conversion and I want to build a new machine with double preloaded ballnuts so I don't have to deal with it.

The problem when cutting circles or curves is that when you reverse an axis there is a short period where the motor is turning but the table is not moving.

When you are cutting the top of the circle (so the y axis is reversing), there will be a fraction of a second where the y axis is reversing and the x axis must stop while the screw takes up the backlash. So every time you change direction the cutter will dwell.

On top of that, it means constant velocity and acceleration/deceleration gets all messed up, and it is a pain to get the machine repeatable and tuned properly since the backlash might not be constant over the entire table.

Mach3 also has some problems with jogging when backlash compensation is enabled. If I had only a thou or two of backlash I would probably go without software comp just to avoid all the random weirdness.

I can certainly cut accurately after spending some time with a dial indicator but I would avoid software compensation whenever possible.

[kensbey]

thanks for all the info guys!

Given all this info, i think i wil try the double nut route. I'm going to be buying 20mm screws from linearmotionbearings2008, so there won't be a huge additional cost involved in getting the extra nuts, just a little more in building the mounts. I'm planning some pretty significant mods to the y axis so that i don't lose any travel with double nuts. with a little luck i may end up gaining some

:banana:

i would like to try the idea of drilling the base and then putting the stepper at the rear, both for asthetics and to save some room at the front. This will probably mean taking the base to a machine shop to mod although, which will probably be outside my budget. any opinions here?

also as for materials, it seems the normal approach is to make screw and nut mounts from aluminium. This seems logical, but the engineer in me keeps screaming about mixed metal corrosion. Ally and mild steel are reletively close on the galvanic scale, but i have always been taught not to mix metals. i'm just a little scared my table will go all rusty :P Metal mounts are possible, but significantly more time and effort to make. I do keep everything coated in a nice layer of inox, so maybe it won't be so bad.

[Robin Hewitt]

Software backlash compensation sounds better than it works.

Agreed. To make it work you have to tighten the Gibbs to a point where they are tight enough to resist the cutting forces, but not tight enough to preclude rapid G0 transits. Then pray they stay adjusted

[691175002]

Ally and mild steel are reletively close on the galvanic scale, but i have always been taught not to mix metals.

I had the same concerns, but I think every hobby conversion ever done mixes steel, iron and aluminium so I figure its a non-issue.