Help-what is reasonable?

On Thu, 13 Nov 2008 18:33:07 -0800, Michael Koblic wrote: [...]

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(IIRC, your machine is somewhat like:

I don't know for certain what the proper approach is for the problem you describe, but here are a few observations that might help until someone gives definitive answers.

-- Backlash will be less of an issue if you consistently pull down or push up on the spindle head when you are using the fine Z dial to lower the head. Otherwise, the spring counterbalance system lets the head move or stick unpredictably in a fairly wide range.

-- Consider using a center-cutting end-mill from the start, rather than a regular drill followed by a square-cut drill.

-- Use a collet or (preferably) an end-mill holder to hold the end-mill; don't try to hold an end-mill in the chuck.

-- Attach a DTI or a digital caliper to indicate depth. Say you want a 4mm or .157" deep hole in 5mm or .197" material. If you zero the indicator when the tool tip touches the work, or set it to -.001" when it touches a cigarette paper on the work, then you will be at desired depth of cut when the indicator reads .157".

-- Make a 4mm thick shim. When the tool tip touches the work, set the limit block (the Z stop plate) by putting the shim between the limit block and the head. I think this will cut out a few steps of your procedure, and should let you mill the holes without engaging the find Z feed.

I think you may be doomed to frustration with trying to rely on the Z axis drive.

You may be able to improve things with a stripdown and some fettling, but probably not. It's the price of small and cheap tools, esp. machine tools.

Consider setting yourself up with a solid, clamp-on stop, that you can use to set the depth that the drill can reach to, if there is not one built in. Once the depth of cut is set by some trial and error, you can then get on with cutting all the holes required. Or use a dial indicator, or one of the cheap digital calipers, to build yourself a crude "DRO" to use when moving the head up and down, and thus separate the movement of the crank, from the movement of the head, if that makes any sense.

Cheers Trevor Jones

Pretty much identical bar minor differences.

The procedure I outlined is supposed to allow for that. Yet the results are poor.

No mills in the house else i would have done. I use No. 22 drill bit but the

I like the shim idea. The problem is that these plates are of rather inconsistent thickness and the depth of cut has to be adjusted individually. I shall look at all these ideas tomorrow. Thanks,

Or just go back to doing it faster and better on a drill press :-)

I am concerned that if I cannot do this simple operation on the milling machine what will happen when I have to face mill etc. to precise depths. I suppose the whole dial indicator thing will come to play. That will mean getting a better one as the one I bought from Samona is a bugger to use - I went through a whole period this morning when I thought the mill was misbehaving when all along it was my indicator.

I have no previous experience with milling machines. Your initial comment suggests that a bigger better machine is less likely to suffer from these issues. Is that correct? I am kind of disappointed as I have seen home-made mills which had better organized Z-depth stop and adjustment than this.

I may have to rethink the whole issue and priorities.

Thanks,

It's simply that to build a milling machine, of any usefulness at all, costs, and in order that the makers meet the price point determined by the purchaser (the guy that ordered a sea can full) they make them to meet that price.

Simply put, there have had to be compromises made, otherwise, we the consumers of these goods, could not afford to enter the game.

Look at your mill as a pre-assembled kit of parts.

You may have to go in and redo some of the work that was not done to a standard that you find acceptable. Such is the way of things.

You may find that you can smooth up the action of the Z axis enough to suit your needs. Track down the play in the works, and see if you can find out where it's moving. It may be something silly easy to fix, like a part not tightened in it's place, or it may be something not so simple to fix. Did it come with a parts diagram? Look it over and see if there are any obvious places that there could be that much play.

IIRC LittleMachineShop.com has some spares as well as some upgrade stuff for these mills. Have you looked at that ? You may be able to pick up some ideas there.

Cheers Trevor Jones

A further thought occurred to me: A pack of cards! However, another issue: To mill properly, I have to lock the spindle, right? I would have thought that the change in Z-depth by the simple act of locking the spindle is quite undesirable, especially as it is unpredictable and of the order of 0.010". Am I wrong?

Right. I did not know what to expect really, nor do I know what reasonable expectations are, hence the whole thread. As I mentioned elsewhere, now I am almost more concerned about the change in Z-dimension when I lock the spindle. It is not an issue with drilling, obviously, but I suspect it will be a big issue when milling.

Lose the circular handle and use the lever handle, assuming you have one. Set a permanent stop, so the spindle stops at the same place every time, then use the knee to achieve the depth you desire. I'm assuming you have a knee on the machine. If not, none of this is relevant.

If you have multiple holes to drill in the same piece, mark your dials and do each operation to all of the holes in each piece before doing the next operation. For example, center drill all locations, then drill all locations, then tap them. If you learn to trust the dials and understand how to mark them, keeping backlash in the proper direction at all times, you can revisit hole locations within a thou with no trouble at all.

Do not use end mills as drills. That is piss poor advice. They, at best, suck for drilling due to their geometry. They evacuate chips poorly, and will cut drastically ovesized holes should one flute load. They are often the cause of mis-located holes due to the end mill moving the table or saddle about when that happens. It's easy enough to grind a flat bottomed drill, which will remove the tapered portion of an existing hole without issues, with no risk of oversizing.

None of this is rocket science, just procedures you'd use on a daily basis if you were operating manual machines. I've done them since the late 50's. No big deal.

Did I mention you should not use end mills to drill holes? :-)

Harold

If you cut a groove or slot, or mill a horiz> -- Attach a DTI or a digital caliper to indicate depth. Say you

I forgot to mention the alternative of setting the zero so that the indicator reads zero when you are at the desired depth. If you do so, then varying thickness of metal you are drilling into won't matter, as long as the surface not being drilled through is clamped against the same reference surface each time.

Put a collar on the drill bit.

(NB if you lock the spindle it changes

...

The new RF-31 I bought for Unitrode shifted by up to 0.005" when locked. I had to mill some shims to better than 0.001" and spent close to an hour futzing with the damn mill without success, then took the parts home and milled them on my Clausing.

The Clausing isn't always accurate in the Z direction either, probably due to wear and the old Wilton vise. I have to tap the work down while tightening the handle, then check the parallels under the work for looseness.

You can change the height of work in your mill with two small adjustable parallels. Set them to some even-numbered size, mill close to finish dimension and measure, raise the parallels to take up the difference. You will need a stop on the fixed jaw of the vise to relocate the work after loosening the vise but that's a good thing to have anyway. I tapped the cast iron on the left end of the fixed jaw and screwed on a small plate that can be swung out of the way. I set the dials to 0,0 with a 1-2-3 block pushed against this stop.

The less you spend on a machine, the more you have to understand and cope with its problems. You learn what it can do easily, or with difficulty, and design accordingly. On a mill-drill the axes may be measurably out of square with each other.

Since the RF-31 wasn't mine I didn't disassemble it or add a Z indicator but I've found poorly machined small parts on other import machinery that were easily cleaned up or replaced. Especially on the older ones it looked like the major parts were made fairly well but the minor ones had been filed out in someone's kitchen. PBS once filmed a family making Toyota taillight lenses at home, apparently a common practice that substitutes for providing daycare.

Jim Wilkins

If you look on sites like CNC zone you will find quite a bit of tweaking info. For CNC operation folks generally ditch the rack and pinion Z axis setup for a leadscrew type drive, and the stock counterbalance is always tossed in favor of something more consistent.

For counterbalance I used a couple gas springs mounted vertically inside the column sticking out the top, with a cross bar and pulleys across the top and 1/16" steel cables connecting to the column and the head. I still have the stock Z setup at present since I was in a big hurry with the project, but it's slated to be changed to a leadscrew eventually.

These pics may give you some ideas. I made this attachment for when I want very fine control over Z depths and tweaks. It can be set up to use the head, table, work or vise as a reference. On a knee mill it allows one to make adjustments to both the quill and knee without losing relative position.

A rod could replace the indicator if just a simple stop is needed. For example, if you want to drill to a constant depth and the workpieces vary in thickness, mount a rod parallel to your drill that bumps the top of the work.

This is the quill stop I made for the Clausing;

No surprise, the rack and pinion drive has to have a lot of backlash. If you want fine control, you need a screw drive of some sort. The rack and pinion is only good for a drill press. You might be able to rig a caliper to the Z axis to measure the position. That will make your positioning much more controllable, as at least you can READ the position.

Does the machine have a depth stop? Most have some sort of clamp-type gadget that can be attached to stop at some particular depth.

Jon

I have worked that one out. The issue is the correect positioning of the depth stop. The shim method which someone suggested seems the best with this machine.

Which is what I have been doing very succesfully on the drill press...

OK, I won't. In any case, there was not a 5/32 mill in the whole of Campbell River today, so I could not even try this heinous crime :-) Thanks,

(NB if you lock the spindle it changes

...

The new RF-31 I bought for Unitrode shifted by up to 0.005" when locked. I had to mill some shims to better than 0.001" and spent close to an hour futzing with the damn mill without success, then took the parts home and milled them on my Clausing.

The Clausing isn't always accurate in the Z direction either, probably due to wear and the old Wilton vise. I have to tap the work down while tightening the handle, then check the parallels under the work for looseness.

You can change the height of work in your mill with two small adjustable parallels. Set them to some even-numbered size, mill close to finish dimension and measure, raise the parallels to take up the difference. You will need a stop on the fixed jaw of the vise to relocate the work after loosening the vise but that's a good thing to have anyway. I tapped the cast iron on the left end of the fixed jaw and screwed on a small plate that can be swung out of the way. I set the dials to 0,0 with a 1-2-3 block pushed against this stop.

The less you spend on a machine, the more you have to understand and cope with its problems. You learn what it can do easily, or with difficulty, and design accordingly. On a mill-drill the axes may be measurably out of square with each other.

Since the RF-31 wasn't mine I didn't disassemble it or add a Z indicator but I've found poorly machined small parts on other import machinery that were easily cleaned up or replaced. Especially on the older ones it looked like the major parts were made fairly well but the minor ones had been filed out in someone's kitchen. PBS once filmed a family making Toyota taillight lenses at home, apparently a common practice that substitutes for providing daycare.

I repeated the measurements and the change is more like 3-4 thou. Between myself and the sucky caliper I got it wrong first time.

I should look at that. However, I tried the shimming and I suspect it is the way to go. I just used an improvised 0.13" shim which gave me one and a half turns of the screw. I can make something up to be 0.145" thick and use it every time. It will give me 2 turns of the screw and for the application it does not need any more. Then the thickness of the plate will not matter: If it too thin for the drill to go through with this shim it would be too thin to use anyway.

That's great. I shall archive these for future reference. Thanks.