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Rabs
29-05-2016, 10:53 PM
Hi everyone,
I have a 1980s vintage benchtop CNC milling machine (Conect Contour Major) that I picked up very cheaply. The axes are in good condition but the spindle is shot. There is noticeable play between the spindle nose and the quill housing which results in ~0.3mm of play at the end of a typical length tool.

I'd like advice on what to do with the spindle.

This is a benchmill similar in size to a Grizzly G0704 or a Sieg X3. At ~200kg it's not tiny, but nothing like a full size mill.


I want the machine to be capable of accurately machining fairly small parts (<100mm in any dimension) in plastics, aluminium and occasionally unhardened steel. I have no current need to machine stainless or any hardened steels. I don't need it to be fast. I don't need it to last forever and I don't mind if I don't get optimum cutter life. I generally do 1-off modifications to relatively expensive prototypes where the value of the work makes fast machining or replacement cutters a non-issue. I'm rarely using the machine for more than and hour or two a week - so please take that into account when answering. This is not a production machine. I often want to use small diameter tools (<1mm). In an ideal world I would like to be able to use a 10mm diameter endmill and a 30mm facemill but having a spindle suitable for the smaller tools is more important to me than the larger end of the range.

I don't need ATC.

I could repair the existing spindle. The motor is in good condition but the spindle itself would need new bearings and quite extensive rework. This would probably be the cheapest option but I'm not keen for a few reasons. 1) The spindle taper is the coventry easychange system, which is uncommon and expensive. 2) The speed is limited to about 3000rpm and I want to be able to use small cutters in aluminium (although I would be happy to use a secondary spindle for this if necessary). 3) I'm not particularly confident that I could dissassemble and reassemble the spindle with new bearings to achieve a low runout.

After that it seems like I have a few options:

A Tormach Bt30 spindle cartridge and modify the existing belt drive to operate it (http://www.tormach.com/store/index.php?app=ecom&ns=prodshow&ref=30505). This will be expensive to import and is limited to 6000rpm, so I assume that I would still need a secondary spindle for small cutters in aluminium and plastics.
A replacement headstock for a common mill like a sieg or grizzly and find a way to mount it. (such as http://littlemachineshop.com/products/product_view.php?ProductID=2636&category=-269978449) This would probably be even more expensive than the tormach but would come with a motor and be easier to retrofit to the machine. This would probably be limited to about 3000rpm.
A chinese 2.2kW or 3kW high speed spindle. I imagine that I will need a better VFD to get anywhere near decent performance from it at lower revs. This seems like the lowest cost option and the only one that I've found that has any possibility to deliver everything I need in a single spindle. However, I would be restricting myself to small diameter carbide tooling for working in steel to keep the SFM up in the orking range because my minimum speed will be ~8000rpm.
One of these: http://www.skyfirecnc.com/picshow2.asp?id=18. Which seems like a pretty good value option but I know nothing about them - has anyone every tried one? How is the quality?
Something like this: http://www.aliexpress.com/item/BT30-Taper-Chuck-1500W-1-5KW-2hp-Power-Head-Power-Unit-CNC-Cutting-Boring-Milling-Machine/32354636148.html?spm=2114.10010108.1000023.9.NGn2x 2. Only for low speed and then a separate high speed spindle. But again, absolutely no idea about the quality of that.


So, in short:
Any other suggestions?
Can I do the work I want to do with only a high speed spindle if I choose the right tooling?
What do you all recommend?

Many thanks

magicniner
30-05-2016, 11:30 AM
Given that they were a perfectly adequate machine I'd repair the existing spindle.
On my benchtop mill I have a 10mm EasyChange Endmill holder and a 12mm EasyChange Endmill holder and use ER11 collet chucks on 10mm shanks and ER16 collet chucks on 12mm shanks as tool holders, this gives really quick tool changes and the collet chucks are cheap so it's affordable to have a rack full with tooling loaded.
Check the manufacturer's spec for the spindle bearings, I got rid of a DC motor that ran to 4000rpm and replaced it with a 3 Phase that runs to 7000 without issues.

- Nick

Rabs
30-05-2016, 01:48 PM
Given that they were a perfectly adequate machine I'd repair the existing spindle.
On my benchtop mill I have a 10mm EasyChange Endmill holder and a 12mm EasyChange Endmill holder and use ER11 collet chucks on 10mm shanks and ER16 collet chucks on 12mm shanks as tool holders, this gives really quick tool changes and the collet chucks are cheap so it's affordable to have a rack full with tooling loaded.
Check the manufacturer's spec for the spindle bearings, I got rid of a DC motor that ran to 4000rpm and replaced it with a 3 Phase that runs to 7000 without issues.

- Nick

Hi Nick,
Thanks for replying. Have you got the same machine? I suspect that we must have slightly different setups. If I did as you do with tool->ER collet chuck with straight shank->easychange holder-> easychange chuck-> spindle the tool would be so far out that I wouldn't have much z travel left, not to mention losing a load of stiffness.

I like the idea of reusing the spindle but I'm really not sure that either it or I am up to it. In addition to the slop in the bearings there is also a load of runout (~0.1mm). I suspect that it was badly crashed at some point and then 'repaired'. The holes for the face pin spanner look like they've been badly abused. I have managed to get it apart but it was a complete pain so I'll need to machine a new one. I don't have any certainty that the spindle itself isn't damaged as well as the bearings.

I don't have an internal bearing pullers or a press to reassemble the spindle with new ones. I also don't have a huge amount of time to invest in the project and need the machine working fairly soon so I am looking for a more 'off the shelf' solution.

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magicniner
30-05-2016, 04:17 PM
I'd be really surprised if you couldn't get a local engineering company to do the press work for you.
My little benchtop mill is based on the Connect Contour, the smaller model than yours I think.
A 10mm Endmill holder gives me 8 1/2" Z clearance, ER11 collet chucks on short 10mm shanks take 1" of that, then add the cutter protrusion of choice.
I've profile cut stainless parts 12mm deep from solid with 6mm single and 2 flute cutters in an ER11 in the 10mm endmill holder, it's not fast but it does it and tool life is OK.


I'm in the process of machining a column to take an Emco milling head for a friend, he has a high speed spindle and it doesn't come down to low enough speeds with high enough torque to do much of what he wants,

- Nick

Rabs
30-05-2016, 07:52 PM
I'd be really surprised if you couldn't get a local engineering company to do the press work for you.

I'm sure you are right but that's not the route I want to go down. It would take a lot of my time (and probably quite a bit of money) to extract all the parts, source replacements, find someone to reassemble it, take it to them and then hope (with no guarantee) that it works and runs true when it get it all back together. Once I've factored in the cost of this and the 2 or 3 easychange holders I'd need to buy it's going to be more expensive than any of the replacement spindles I'm looking at. So, as I say, I'm not going to try to repair what is there at the moment.



I'm in the process of machining a column to take an Emco milling head for a friend, he has a high speed spindle and it doesn't come down to low enough speeds with high enough torque to do much of what he wants,
- Nick

That's interesting. Do you know where he got the milling head? Does someone sell them as spares? One of the problems with my list is that most of them are coming from overseas, so if there is a UK supplier of spare parts for a suitable mill then that might be a good option.


Thanks for your help

magicniner
30-05-2016, 08:30 PM
That's interesting. Do you know where he got the milling head? Does someone sell them as spares? One of the problems with my list is that most of them are coming from overseas, so if there is a UK supplier of spare parts for a suitable mill then that might be a good option.

I don't think it would work for you, it's small and you'd have no-where to mount a motor, it's not an "off the shelf" solution.

My suggestions were all aimed at getting it up and running as quickly as possible with the least cost and the best overall machining capacity.
Buy a spindle that fits where the old quill went and live with the speeds/torque/tool capacity you get but don't throw away the old bits, they will enhance the resale value,

- Nick

m_c
30-05-2016, 11:53 PM
Are the original bearings noisy?
If they're not noisy, I'd try adjusting them up, and then test it again. Even if you just tighten the one ring to remove play, it'll give you a far better idea of what condition the spindle is in.

As for potential replacements, it'll depend on the space available. Do you have any photos of the existing head?
Personally, I'd be looking at something that makes tool changes reasonably easy, like a BT spindle, so you can swap tools without having to worry about setting tool lengths.