[Numb Nut]

Hello everyone!

I'm a total newbie and have been lurking on here for a short while with the idea of getting a milling machine. I eventually treated myself to a new XJ20 milling machine. Well it's arrived and is sitting on the garage floor!

I was just wondering if someone who is perhaps familiar with this machine can give me a quick run down on what I should do in terms of basic preparation? By this I mean, what bits should I open, clean and lubricate.

I'm such a newbie I had to ask the seller how to open the drawbar cover! Turned out that it was painted over and needed to be hit with a block of wood! :withstupi

Also, I hear that like many of the cheaper imported machines, the XJ20 is shipped with free swarf hidden inside and owners have to try to find it so they can unlock the special bonus - a usable milling machine. As I'm crap at games (with the exception of "Monkey Island" but that was a few years back) I'm hoping someone can help me cheat...

[iGG1e]

Initially just clean off the protective grease from the table and the slideways, then give them an oiling. If you don't want to dive too far into the mechanics of it then I'd just make sure the gibb strips are cleaned, oiled and re-adjusted.

You now need to tram the head and also if possible check the quill/spindle to make sure it's not suffering from the alignment/wobble/run-out some of us have found. I'd also keep a close eye on the state of the gears by periodically shining a torch through the vent holes on the right side of the head casting. If you start seeing gold coloured flakes, then it means the drive gear is wearing and will eventually strip it's teeth completely.

Did you get an R8 version? Bear in mind that the supplied draw bar thread is metric for some reason and when you come to stick in 'normal' R8 collets etc they won't work as they use a 7/16-24 (from memory) thread.

Besides a few problems, for the size they can be a very productive machine.

[Numb Nut]

Many thanks for the helpful answer, iGG1e.

Mine's the MT3 version which I think has a 12mm drawbar thread. Say, are there any significant advantages/disadvantages favouring R8 versus MT3?

I cleaned off the grease from the table using a rag and found that there were a couple of areas of deep circular scratches - both at the front edge and the back edge - midway along the X direction. Should I expect the table to be free from such marks?

The instructions recommend to use "stove distillate" to remove the protective grease. Not sure what stove distillate is - is white spirit okay?

Ok - I'll have a look at taking the table apart to clean and oil the gibb strips.

And I'll need to do some reading up about tramming the head too.

I've noticed that the spindle has a horrendus amount of movement side to side if unlocked and this gets worse when lowered. With a lathe there's typically no movement in the spindle, I would have expected the milling machine to be similiar - can this be adjusted out?

Thanks again for your help!

[Numb Nut]

I had a go at measuring the quill wobble and found that it increased as the quill was lowered and also increased if I used more sideways force.

Using a light hand on the unlocked quill and putting a plunger dial gauge on the side of the collet holder, I measured the following:

0.009" (0.23mm) quill raised and unlocked
0.025" (0.64mm) quill lowered and unlocked, held with fine feed clutch

By locking the Z, the quill wobble was almost eliminated.
Edit: actually I mean locking the quill

To test spindle run out, I put the dial gauge plunger against the taper just above the collect holder and rotated the spindle by hand - there was minimal needle movement.

Any feedback on these figures would be appreciated.

Just out of interest - what sort of figures would be expected from a top end quality machine?

[Numb Nut]

Here's a couple of pics showing the scratches on the table. Do other XJ20 owners have similar damage on their tables?

[HackMax]

Using a light hand on the unlocked quill and putting a plunger dial gauge on the side of the collet holder, I measured the following:

0.009" (0.23mm) quill raised and unlocked
0.025" (0.64mm) quill lowered and unlocked, held with fine feed clutch

By locking the Z, the quill wobble was almost eliminated.

Sounds like you need to tighten the z gibb. It may be a tad loose. I have an X3 and I was getting the same kind of specs from it until I tightened the gibb. It got a lot better but if I put pressure on the head by trying to lift it I can see it and feel it move on the dovetail ways. I have tried tightening the gibb more but then I can't get the head to move all the way up the column. The problem is if you have too much wobble here there will be consequences in the finish of the machined part and for what I need my mill for the the better the finish the easier it will be finalize the part. I can't figure out why when the head gets towards the top of the column it wants to bind somewhere. At this time it's not important that the head gets that high but eventually I'll have to do something about it. As it is I need to leave the gibb a little loose so that it will get to the top.

Rick

[Numb Nut]

Sounds like you need to tighten the z gibb. It may be a tad loose. I have an X3 and I was getting the same kind of specs from it until I tightened the gibb. It got a lot better but if I put pressure on the head by trying to lift it I can see it and feel it move on the dovetail ways.
Rick

Thanks for the reply Rick!

I was rather clumsy with my wording earlier - I said "locking the Z" but I really meant "locking the quill" - sorry about that! The spindle movement in my mill is almost entirely in the quill - it's much reduced if the quill is locked.

As it happens the Z gibb adjustment screw is only hand tight in mine and the extra movement measured at the chuck when pushing and pulling on the side of the mill head is under 0.002" (0.05mm) between locking and unlocking it.

Do you have a way to lock the mill head to the column? I assume this would eliminate the movement you are seeing as a consequence of having the Z gibb loose?

[HackMax]

Yes I can lock it up if necessary and have to when I use my face mill or fly cutter. Since this is a CNC machine there aren't many other times I can do that though.

I always keep my quill locked and unextended unless I need to do some manual work or set up for a part. The lower the spindle the more flex you introduce. These machines are small and pretty light weight so the more rigid you can make the thing the better the finish on the part. I have an idea I think I might try to give the z axis more rigidity. Along with a counterweight system I'm going to try to add a follower cam bearing under the head so that it contacts the column and relieves some of the pressure on the ways. This should allow me to tighten up the gibb a little more.

Rick

[iGG1e]

Cleaning can be done with anything that'll help shift the grease. I used WD40 to clean mine up and lubbed it up with way oil afterwards. The reason I went for R8 instead of MT was because I knew I'd be getting another mill with R8 a couple of months later and didn't want to double up on tooling systems.

I'd say the scratches are par for the course when it comes to Chinese mills. You should see the dents, yes dents, that the animal at the factory put in the table of the SX3 when they bolted the 4th axis on for shipment. These tables are soft and it doesn't take much to damage them.

There is no adjustment for the quill with respect to the head casting. Ideally there should be no wobble, but this just isn't the case with these...they vary wildly. The effect is obviously a lot less when it is locked for milling at a level, but when it comes to drilling and plunging etc, it does create a problem. From your figures it sounds like it is the fit of the quill in the head giving you the problem. When I locked my quill with the DRO on I could see a change in the reading and Hugh sent me a different head. Luckily through mixing and matching I got a good fit.

Rick, I'd be interested to hear your ideas on adding rigidity to the X3 column. The head side plates do seem to get in the way nicely of an easy fix!

[Numb Nut]

Appeciate the info on cleaning off grease and the table scratches, iGG1e.

Sounds like I should be happy there is something resembling a X-Y table at the bottom of this machine.

If anyone fancies measuring their machine's quill wobble when it's unlocked, raised and lowered, I'll all ears... I mean eyes!

[HackMax]

Rick, I'd be interested to hear your ideas on adding rigidity to the X3 column. The head side plates do seem to get in the way nicely of an easy fix!

Well I've been toying with this idea for a while after I noticed the slop in the head and was trying to adjust the gibb to remove it. If I place one or more of these under the head and jam the bearing up against the column this would better align the dovetails so that I could tighten the gibb more and also help with tramming the head. The surface that the bearing would be riding on is more than adequate. The only issue maybe is keeping the column clean but that can be solved by using a bellows or similar. I also don't know how thick the underside of the head gearbox is and the consequences of drilling up into it.



I haven't drawn anything for the counterweight yet but it should also partially relieve the stress on thew column if the weights were placed towards the back of the machine. It would use two pulleys, a cable, a mounting bracket for the pulleys and the weights. I really need it to help out on the stepper motor though so thats the main reason I'm using that.

Rick

P.S. I haven't figured out how to put pictures here yet (chair)

[Numb Nut]

Rick - what you said about trying to use the quill raised makes alot of sense. For some reason I assumed a CNC machine would raise and lower the quill but it makes more sense (from a machining tolerances point of view) to raise and lower the entire head.

I notice that with the quill on my XJ20 the movement is really due to the gap between the inner and outer steel tubes. Not sure there should be a layer of paint on the inner tube but I'm thinking that if this was a thicker layer then it would eliminate the slop that I'm seeing. Perhaps if I were to put a shim in there?

[Numb Nut]

P.S. I haven't figured out how to put pictures here yet (chair)

Try this - when you add or reply to a post, click on "manage attachments", then in the new window, click on one of the "browse..." buttons and locate your picture. Then click on "upload" and when it's done, click on "close this window" at the top. Then when you hit submit, your post will have the pictures attached.

[HackMax]

Try this - when you add or reply to a post, click on "manage attachments", then in the new window, click on one of the "browse..." buttons and locate your picture. Then click on "upload" and when it's done, click on "close this window" at the top. Then when you hit submit, your post will have the pictures attached.

Cool, thanks!

Rick

[iGG1e]

The gap at the top is above the actual area in the quill where the top bearings are. If I remember correctly the black looking cylinder is basically a sleeve to hold the return spring.

Dropping the quill out requires you to take off the feed mechanism on the side and then from the top push down the black sleeve to take pressure off the thick C washer so you can extract it. Then the quill will drop out...if you've not allied the lock! This might give you a better idea which bits are wobbling.

That's a nice idea Rick, but like you said, making sure nothing can get between the bearing and the column to compromise the smooth rolling is important. I'll have a look at mine to see if it's a viable addition to the rest of the mods, but the rotating head design might give a few complications.

[HackMax]

That's a nice idea Rick, but like you said, making sure nothing can get between the bearing and the column to compromise the smooth rolling is important. I'll have a look at mine to see if it's a viable addition to the rest of the mods, but the rotating head design might give a few complications.

Ahhh You have the SX3 I gather? I was thinking of getting that model but really the only thing I would need from it is the ability to rotate the head. Then I gathered some info on the building a 4th axis for the X3 and found it was cheaper to implement the angle that way plus the added benefit of getting computer control of the rotation.

I was also concerned with the added weight of the head with the rotation design and the flexing of the column. I believe the columns are the same on both machines. I figured if the column is good enough for the SX3 then it would be super OK for the X3.

I don't think my idea would work for you machine.

As far as keeping the surface clean I was also thinking of putting some sort of bracket or box around the bearing with some 1/8" thick felt on it so it could wipe any surfaces clean just in case.

Rick

[Numb Nut]

Yet another newbie question - is the 4th axis the ability of the head to tilt over from left to right? :idea:

[HackMax]

Yet another newbie question - is the 4th axis the ability of the head to tilt over from left to right? :idea:

Well it depends on where you design it to work. I've seen small mills where the column is actually tilted. I've seen big mills where the head is tilted. But for the most part it is just a rotating plate you set on the table of the mill so you can mount your stock to it and do the angle milling.

Then there's the 5th axis... lol

Rick

[iGG1e]

I think the term 4th axis is generic and most people assume when you're talking about a convention style mill XYZ, that the 4th is going to be the CNC controlled rotary table. The A axis.

Rick you're correct, it is the Syil CNC modded SX3. I'd love to have the column a bit more rigid, but as it is it isn't too bad if you keep your DOC values a bit lower than you might want. The U channel type column and the head assembly makes it difficult to come up with a simple stiffening solution. I'm going to see if there's any way I can mount a backbone of heavy square section to the column and base without it interfering with the Z movement.

[Numb Nut]

Found a useful explanation of 5 axis milling/turning - about 1 min from the start of this video:

http://uk.youtube.com/watch?v=_4vLqfIx8X8