View Full Version : CONVERSION: CNC Arboga U2508 Mill Conversion

18-03-2012, 10:24 PM
Right then been a very very very quiet on the build front for a good while now for very good reason. To remedy this i thought i would kick off with what the immediate future plans are.
I need to downsize my workshop a bit to move stuff out of the house to make way for our new arrival (no not the new mill?). To do this i took the decision to sell the Bridgeport as that take the most room up and if need be i have access to another. It really pains me as that is my favorite toy :cry:. Before i have had chance to list her i got the chance of an Arboga, great machine but does come with some challenges. It is in great shape and now in pieces on my workshop floor ready for when i can start.

Bad points:

1. 415v two speed motor - found nothing to say i can rewire for 240v, many have tried
2. Spindle has an MT3 taper with a locking ring around the base as there is no way to put a draw bar because of the gearing above (my locking nut M62x1.5 is missing so will need to make a new one)
3. The drill chuck is stuck in the taper (looks like it has never been removed since new)
4. Table is not massive

Good points:

1. Very sturdy machine and knocks spots off most medium size mills, even modern ones
2. Big enough for most things i play around with
3. Everything is metric
4. Takes up very little room
5. 20" of gap between bed and spindle for those tall jobs
6. Lots of space to hide anything and everything
7. Quill has 140mm of movement which means i can run that as my Z and leave the column manual for different job sizes


1. Strip it down
2. Clean and repaint machine
3. Make a new nut for the M62 thread (In case i need anything MT3)
4. Make an ER32 collet holder to fit over the M62 thread instead of using the MT3 taper
5. Pull the motor windings that are built into the machine and retrofit the guts from a 3phase 1HP 2800rpm doner. I will loose the two motor speeds but will get this back from the VFD control and will still have two mechanical speeds to play with.
6. Use 20x5 ballscrews on the X and Y. Still not made my mind up about the Z?
7. May need to make some new gears for the head but until i get it running will not know. The ones i may need to replace will be made out of tufnol. This will keep that head nice and quiet.

So far:

1. Purchased machine
2. Ordered ballscrews
3. Sourced new switches and things
8. Have a 3phase motor (only 1400rpm) to test theory of swapping over gubbins.

This is not going to be a quick project as my new son is due home next week after being born 9.5wks early. This has taken most of my time up as i have been left to look after the other kids and work full time. In the end i may loose my bridgeport which i still need to sell but will have a CNC mill.

Lets see if i can be better at updating this log with more detail and pics than before :tup:

John S
18-03-2012, 10:39 PM
Answers to plans.

3/4: Don't bother, hit and miss whether you will get run out from just a thread and no register.
Instead get a standard MT3 ER32 collet chuck and machine a groove in it with carbide tooling and fit a circlip to hold the washer and the M62 nut.

BTW I have a short threaded test piece with the Arboga thread on it, OK if you want to borrow it or if you are dead stuck I can make you a threaded sleeve.

5:You could always buy a 440 v 3 phase VFD feed it 440 v single phase from a yellow brick wired backwards and the earth centre tapping removed and use this as 440 v in but de-rated. You can pick 440v input vfd's quite cheap

18-03-2012, 10:54 PM
Hi John

I did look at the options for the motor similar to what you are saying but i like things to be neat and tidy. The casting on the head fits a standard frame so should not be an issue swapping the guts over from a doner motor. I may even find that i can pull some more wires out on the existing (split the coils) which only has 6 coming out? will get to that once i can pull it. As for the tooling like you say just mod standard arbors but will still have a go my way as it will make things nice and easy, with an er chuck and a facing mill should not need much else.

Back to the motor if all else fails i already decided just to chop the lot off the top and fit a motor on top with a pulley going to the spindle. I can then fit a draw bar :naughty:

John thanks for the offer of the test piece but i should be ok on that front.

18-03-2012, 10:58 PM
Look at bottom pic and you will see what i mean....http://www.lathes.co.uk/arboga/index.html

Robin Hewitt
18-03-2012, 11:45 PM
3. The drill chuck is stuck in the taper (looks like it has never been removed since new)

That doesn't sound good, especially if your chuck extractor isn't good and hard.

Gi' it some wellie, hope they didn't use Loctite and if all else fails call out the fire brigade and see if they have something hydraulic :naughty:

19-03-2012, 12:14 AM
Should be fine robin as it has a knockout in the side of the quill.....but yes a bit of welly will work nicely

21-03-2012, 11:04 PM
I've promised myself some time next week so will start the clean up and get some pics up of how she looks now. Come up with very dark grey colour almost black and maybe a hint of green here and there? I know painting is not the be all and all but better to get that done whilst i have a chance or like everything else once it is together it will stay that way......I really do need to clean up the shop though and start getting rid of the rubbish...I hate cleaning.

Still waiting on the screws to arrive for this one and still mulling ideas about the screw needed for the Z'd if i go down that route. Looking at it though i may be easier to replace the pinion gear that is there and work some way of tensioning it to alleviate the backlash?

16-02-2013, 06:35 PM
Did you get much further I am just going to start a similar conversion on my Arboga and would love to hear of your progress
Geoff Cape Town

18-02-2013, 10:14 AM
Hi Geoff the short answer is yes and it is not the easiest conversion on the planet if you want to do it right. There is not a lot of space for 20mm ballscrews under that table. I've dumped the gearbox on top and going for two speed direct drive on VFD. Expect to do a lot of machining of the table. Not really a job unless you have access to another mill. I have had to build a complete new inner spindle to give tool release (it will accept R8 as well).

The project has been on hold for a while due to other circumstances, i will get back to this thread properly as soon as i can.

03-04-2013, 11:07 PM
About time for an update and a drip feed of pics. Tonight I finished rebuilding the spindle for this machine in readiness for the Poly v pulleys i need to make. I dumped the original inner and used an old spindle from a lever lock collet closer. I re machined it to take new bearings and machined it to use R8 tooling (before you ask why?....i have loads of it already). I ended up with a 28mm id bearing on the top and needed a lock nut, apparently they don't do them? So i ordered a 28mm x 1.5 pitch hub nut for a citron/ Peugeot that fitted the bill and sunk a capcrew in the side and slit it. It locks lovely


The next job is to make the pulleys and machine the rest of the spindle so it all looks good.

03-04-2013, 11:12 PM
Another pic of the R8 end8643

07-04-2013, 11:01 AM
:friendly_wink::friendly_wink:What size and type bearings did you use if you dont mind me asking? Still collecting info for my spindle project and its good to build up a data base of existing arrangements.

You are probably aware but the pinch bolt in the top lock nut could cause vibration and imbalance at high speed, since you mentioned vfd I'm guessing you are looking to increase top speed? If not ignore my comment :friendly_wink::calm:

08-04-2013, 09:25 AM
Hi Ross

The lower bearing is 35 x 62 x 18 and the top bearing is 28 x 52 x 12. I've left enough room to double the top bearing should i need too. It's all about making things fit, it does not work out then i shall build a complete new spindle and housing. The locknut should be fine as used that arrangement before on another project. It's all heavy duty so will have to see how it works out. Just made a new adjustable burner for the furnace, so will get some Ali blanks cast at some point this week to make the pulleys. I can then start getting the motor mounted etc.


08-04-2013, 06:50 PM
The locknut should be fine as used that arrangement before on another project.

Fair point, just seems a shame to do all that work and then risk an imbalance problem :smug:

Cheers for the bearing info, are they AC or deep groove?

lastly why would you want to put 2 bearings at the top? most of the cutting force is in the lower bearing, hence the lower one being bigger.


08-04-2013, 09:29 PM
The top are just deep groove, having two just helps with stability. As for the nut i could always replace that without too much effort. Thamesdown bearings said they could get me proper locknut but only on as a special order for a ton of money. I will learn a lot more from what does not work, i'm happy to just plod along :lemo:

I did my casting today for the pulleys as one of the kids had a teacher training day. I had the first pulley on the lathe tonight and ruffed out. Need now to switch to the 4 jaw for the finishing cuts. Before i can do that i need to make a new mount for the lathe theres always one more job that gets in the way......

09-04-2013, 12:59 AM
Hi Swarfing, apologies I seem to have ended up critising your design when you didn't ask for help. duh

I just have an inquisitive mind and when I see something different I have to ask just in case they know a special trick :smile::smile::smile:

Based on what I have read from other threads I think you might have problems with using deep groove bearings preloaded against AC, but I wont mention anything about that. :smug:

with regard to the lock nuts can't you just get 2 more of the wheel nuts and face them down to 4/5mm thick on your lathe?

09-04-2013, 08:22 AM
Ross don't apologise for having an opinion thats a good thing. I'm replicating what Arboga had in the first place (who am i to argue). I plan to build a complete new head at some point so just want to get the build finished, this allows me to carry on building with roughly the parts to size needed. I'm waiting on some hydrolic Tubing to make up a complete new spindle (when he gets some in of the right size).

09-04-2013, 06:56 PM
So is the standard set up an AC bearing at the bottom and then 2 deep groove at the top? sounds a bit strange. for 2 bearings at the top I would expect a roller bearing at the bottom (radial loads) and then 2 opposing AC bearings at the top (axial loads).

I know what you mean about getting it working to then build the upgrade parts. Sounds like we are doing very similar projects. I think I will watch your progress and learn from your mistakes.:biggrin:

09-04-2013, 07:01 PM
No it is a taper bearing at the bottom

10-04-2013, 01:20 AM
No it is a taper bearing at the bottom

Ok that makes sense, deep groove bearings pre-loading a taper which can take axial and radial load. I would have thought an AC at the top would have been better as you still get the speed increase from using ball bearings but not the heat issues with pre-loading deep groove bearings, (as you are forcing them to run on the edge of the race) excessive heat will cause expansion and reduce the pre-load on the bearings and therefore rigidity.

This is the theory so it will be interesting to see if in a hobby environment it is actually a problem. that is what I'm trying to find is the balance between the ideal design and what works in practice.

12-04-2013, 11:17 PM
Monday i had a chance to cast some Ali blanks for the pulleys. Got one machined up yesterday evening and the other tonight. The one on the left i will have to make again. Stupid me let go of the cross slide whilst plunging the pipe threading tool in for the ribs and it pulled itself in (tool slightly too low). This in turn locked and flung the pulley out of the chuck damaging it. I will use it for now so i can mock things up.


Made these to fit 'J' section 5 rib belts, size 559mm long or 22" in old money. Belt will be here next week.

12-04-2013, 11:41 PM
looks good, shame about the slip, why is it always the last operation that goes wrong?

when will it be working then?

13-04-2013, 12:01 AM
Good question? Time is very finite that i can use so it really is a question of slowly but surely at the moment. Need to do some casting which i will do over the weekend hopefully. I can then build the motor supports and remake the left pulley. Now i have these bits i can start laying the motor out and fix the top plate, work out how i'm going to fix the spindle in place as well as make a bush to lower it in the head slightly.

Will grab some more pics of all the other bits as soon as.

19-11-2013, 02:44 PM
Did you ever finish the conversion? Thinking about doing the same on my old EM825.

20-11-2013, 07:31 PM
Hi Tojan

Ive completed the table with screws etc, fitted the head and just need to sort the gearing for the column (z axis). Things have been very slow due to family commitments and troubles this year. Could have used it a million times over already.

If you did go down this route i would recomend 16mm screws, and don't even attempt it unless you have access to another mill and lathe.

20-11-2013, 10:04 PM
Well thanks for the reply. Any more pictures of your project would be really helpful. This is my first mill, and I'm just getting finished rebuilding it. I've got the bug to build some stuff that can't be done manually. Unfortunately I don't have access to another mill, I do have a lathe.

21-11-2013, 06:17 PM
You would definatley need access to another mill. I had to take quite a bit out of the table and mid bed to accomodate the ballnut, There is very little difference between your and mine. Being more carefull than me choosing the right type of nut, you maybe get away with not machining but it is tight. If i get a chance i will grab some more pics with some details. I decided in the end to utilise the rack and pinion on the column and reduce with a 72:24 pulley. Not a lot of room to mount on the back of that column though.

04-05-2014, 06:18 PM
Did you get much further I am just going to start a similar conversion on my Arboga and would love to hear of your progress
Geoff Cape Town
Hi Long time since I posted to you so here goes.
My Arboga conversion is now operational. Still to fit are guards and some kind of spring or counter weight to the Z axis
I used 2 to 1 reduction belt drives with nema 25 425oz motors.
I have reasonable back lash on y and z axis but 3 thou on the x axis.
I am thinking about upgrading to ball screws on x and y and a screw z conversion in order to get rid of the machines worm drive.

Have you a recommendation you would share with me.
I am at the moment in the US visiting my son and thought it would be a good idea to get bits over here and save the hassle of shipping and duties that make life difficult in South Africa.
I came over at short notice so I did no measurements.
After getting pulleys,belts,stepper motors and a driver board it took about 6 months to get it done

Geoff Ford Cape Town

12-05-2014, 01:13 AM
Hi Geoff sorry for not coming back quicker as i have been snowed under rebuilding my workshop and other things so my build had stalled quite a bit. On X and Y i went for 16 and 24 HTD5 15mm pulleys and belt, as for the Z i kept the existing rack and pinion and added a plate with a bearing fitted. To this i a have 72 toothed pulley with a 16 on the motor. As for the screws if i could do again i would have just gone 16mm instead of the 20's as it would have been less hassle and im sure up for the job. I did consider mounting a screw for the Z in the base mounting the ballscrew to the base of the column but would have been quite a big job with conventional tools. I might still do this when the machine is up and running as i can make the parts on it. I'm using the similar motors to you and they should be fine. Hope this helps a bit?


30-09-2015, 12:46 PM

There has been some discussion about ballscrew conversions on the arboga.
if you have a look at this link
https://www.damencnc.com/en/components/mechanical-parts/isel-ballscrews-16mm dia.
they sell a low profile easy mount ballscrew assembly.
May be of some help