Keeping the head from turning on a cheap mill

[CrazyModder]

Hello,

I'm using a cheap mill (known as "HBM 16" over here in Europe). It mostly does OK for me, but if I'm milling very heavily then the column may start to swivel slightly. This can lead to rather drastic results, the least of which being a bad mis-cut, and any X/Y numbers being invalidated.

I've attached an image of the machine. The culprit is the clamping mechanism at the base - no matter how tight, it still allows the column to turn if the force is too large. The column is very smooth, after all.

I'm thinking about boring some holes into the column in a straight line (maybe 1" apart), and one hole into the base. Then I could insert a tight-fitting pin to keep it from turning. But I'm not sure if the column might warp a little bit from all the holes, or if the forces may rip the base apart (probably not, but who knows).

The column is 70mm (~ 2.8") in diameter and solid.

Thanks for any comments! Did anyone here solve this problem on a similar machine?

[BillTodd]

You're asking abit too much of that mill  IMHO.  Check your feeds and speeds.

Most of the fixes (including my wishbone stabiliser)are to keep the head alignment while lifting or lowering the head.

Drilling and pinning will only show up the lack of rigidity of the design i'm afraid

Bill

[Swarfing]

A question? is the rack fixed on the column or does it float like a pillar drill? I have an Arboga where the rack is fixed and there is a jib to the side of it to take up the slack. If it is a floater then you could look at fixing the rack to the column and fit a jib strip. This is just a suggestion only?

[CrazyModder]

@Bill, I'm aware of the limitations of the machine, and am taking a pretty long time with most cuts. But it does work well for me most times (roughing end mills make mild steel seem to be pretty soft...). I did replace the hollow column with a massive one, and that helped tremendously.

The problem occurs when I am just at the border of (in)sanity (with regards to depth of cut ;) ), and the swiveling creeps in slowly without me noticing; most times the workpiece is ruined then (especially when using flood cooling so I don't see much). I've not done the pinning because it seems pretty unsatisfactory to me - for once it will only allow "stepped" heights of the head. And I'm really not comfortable drilling holes into the base itself. Hence, looking for more ideas. What do you mean by "show up the lack of rigidity"?

@Swarfing, the column is losely coupled with the base and with the head. The base is slotted and must be clamped with the small(ish) screw that sticks out to the left, thus grabbing the column. The head is clamped to the column with some other mechanism that seems to hold pretty tight. The base clamp is opened to move the column+head up or down; the head clamp needs only to be opened to rotate the head. The head does not move up/down on the column.

The problem occurs in the base clamp, not in the head clamp.

[BillTodd]

+The problem occurs in the base clamp, not in the head clamp.

Ah! In that case pinning would be a fix:)

Bill

[SwarfnStuff]

Since, (to me anyway) it appears that the column moves up/down to set depth of cut, could you cut a key-way in both the column and base then fix a key to the column? This would prevent twisting but still allow vertical travel.
John B

[CrazyModder]

The keyway would be perfect, but is sadly out of reach of my capabilities (especially the slot that has to be cut into the base). If I give that work out to some contractor, it would certainly cost more than a new machine. 

[chipenter]

Just replace with a bolt and use a spanner , or fit a thrust bearing under the head .

[Arbalist]

If the rack on the side of the column is fixed both ends it shouldn't move that much. Can you take a picture of the elevating mechanism and rack so we can see exactly whats there?

[Arbalist]

It may be worth contacting this guy as he's done a lot of mods on his.

http://www.juergenschwelm.de/

He seems to speak English? so hopefully conversing with him should not be a problem.

Another link:

http://hpeters.home.xs4all.nl/cnc/hbm16cnc.html

I've not seen such a lightweight version of a mill drill like this before with no fine down feed. They seem to be popular in Germany though and folks are making some good stuff on them so your problem must be solvable! Please let us know how you get on.

[CrazyModder]

If the rack on the side of the column is fixed both ends it shouldn't move that much. Can you take a picture of the elevating mechanism and rack so we can see exactly whats there?

The rack is, sadly, not sitting tight in its slot; some people have actually retrofitted a guide there so the column can be moved up/down without swiveling. This is fine - when moving the column, no sideway forces act on the rack. But, frankly, I would not want to have the rack take up much force during milling if it can be at all avoided as it has structural function - if the bottom clamp is opened, the rack takes up the considerable weight of the column and the head...

I'll see if I can get photos of the clamping mechanism, but it's just a bolt with a handle that compresses the slotted base around the column.

It may be worth contacting this guy as he's done a lot of mods on his.

http://www.juergenschwelm.de/

He seems to speak English? so hopefully conversing with him should not be a problem.

It's no problem, especially as I'm a native German speaker as well - in fact we're chatting regularly in a German forum. ;) He did indeed do several very nice improvements to his mill, but has since sold it for a larger one.

I've not seen such a lightweight version of a mill drill like this before with no fine down feed. They seem to be popular in Germany though and folks are making some good stuff on them so your problem must be solvable! Please let us know how you get on.

Yes, it is an extremely low-cost mill/drill. Out of the factory, it can hardly be used for milling since it comes with a very thin-walled column (like 3mm or 1/8" wall thickness) - usually the first thing you do is to replace it by a solid column. And it has absolutely no "comfort" features at all; even all of the scales are unusuable because they're just some bolted-on metall strips; the chinese do not even bother with lining them up correctly. ;) But some people like to improve the machine - it costs almost nothing (hence, no risk of damaging an expensive tool) and you learn the basics of machining the hard way, if you're that inclined. The fine down feed is a popular addition, as well as DRO, fluid cooling, 3-phase motor etc., some people even pour the base with epoxy cement for additional weight...

I guess that any round-column mill/drill is facing the problem I'm trying to solve here, so I was hoping there is a "standard" solution. But extensive searching did not turn up anything so far; I guess people are rather tending to get a larger mill without the round column, and using this only as a drill.

[Swarfing]

On one of those sites i got a better view of the base. If it was my machine i would sink some more holes in that rack to secure it better to the column. You don't need to use massive screws, don't be afraid to drill through the teeth. then just above the riser handle in the column support casting sink and tap a hole up against (side on) the rack. make this the biggest you can get away with and use a brass caphead or grub screw to act as jib keeping it from turning. then from the drill another smaller tapped hole to fit a small grub screw to lock the brass one in place. i hope that all makes sense.

[Jonny]

Its a generic RF25 similar to many other branded ones sold by Chester, Warco, Machine Mart, Sealey and so on.

Just got rid of mine purely due to lack of space and not used for last 9 years, it was one accurate machine with limitations.

Even milling 4" x 2" aluminium 26" long sticking out a Chinese cheap vice by 11" the head never twisted the vice back broke out.
Don't bother pinning the rack its useful way of increasing the travel from 14" in X axis.
I used to leave an 1/2" drive socket and ratchet by the side to tighten the head tight. If the tubes rotating in the bolt on base could try drilling and tapping say M8 through casting in to the tube. Is the solid replacement undersize? If so probably the problem also could try some bearing retainer Locktite.

[BillTodd]

Have a lookat this triangular gib key (scroll down the page) www.lathes.co.uk/metalmaster/

[Arbalist]

Its a generic RF25 similar to many other branded ones sold by Chester, Warco, Machine Mart, Sealey and so on

Take another look at the picture, it's not the same as a RF25. The head stays clamped to the column on CrazyModder's HBM16 and both are raised and lowered together by the crank on the base. If he were to bolt the column to the base as suggested he wouldn't be able to raise or lower the head with the crank!

[Arbalist]

I guess that any round-column mill/drill is facing the problem I'm trying to solve here.

No, not really. If you can get one of these they are very good by all accounts and don't loose registration like the Chinese ones. Sadly the RF25 and clones changed a pretty good design to avoid having to supply a cabinet with the machine into which the column goes up and down like the Ixion or later Naerok machines. In the process they created a flawed design. I nearly bought an Ixion, it's a very well made machine.

http://lathes.co.uk/ixion/

[CrazyModder]

Thanks for all the comments.

No, the RF25 is indeed another design, as far as I can tell - on that machine, the column seems to be fixed to the base; in mine, the column is fixed to the head. (In regards to vertical motion - the column-head can be loosened to allow 360° swiveling of the head).

The battle plan looks like this now:

1. Simply roughen the column a bit. It is extremely smooth; maybe sanding it a tiny bit, just to change the surface, is enough to get some tension.
2. If that is not enough, add a few bolts to the rack, and figure out some way to guide it.

[Arbalist]

Sounds like a good plan. Any chance you could get the column sand blasted?

[CrazyModder]

Good thought, I'll check that out.

[Jonny]

With you now, only the base and no through feed through head are different. My drillers the same and a right pain last used 22 yrs ago, rack pinned.

Roughing it up wont do much, worst case you will be reducing diameter and less grab.
Some form of robust cylindrical clamp needs making much like reverse idea of RF25. Junk that toggle single clamp. Easiest If base is a casting, 4 billets cast welded on back to put two M12 bolts through. Then saw down middle of casting extending the slot that's already in for toggle, so it closes up on column over a wider span.

[CrazyModder]

I fixed it, and it was dead simple: I just had to strip off the paint under the bolt head at the base. Obviously, the extremely thick layer of primer+paint would compress and thus loosen up ever so slightly under extreme circumstances. Since sanding the base completely clean there, I have not managed to turn the head during milling.

[Arbalist]

 Pleased you've got it sorted! 

[superc]

Hi.  I would give some consideration to filling the hollow column with epoxy and sand, then drilling the column for the cross pin.

[CrazyModder]

Nah, the column is massive steel, I replaced the stock one before even starting it up once. ;)

[velocette]

Hi
Lots of ways to fix the problem posted here so I will add one more. Replace the clamp bolt for a one with a finer pitch thread this will give more closing pressure for the same amount of torque.
 The roller thrust bearing under the nut is a good addition.
 Keep the column clean

Eric