Having trouble boring Parallel bushes for Z axis on my router project

[DMBGO]

Hi my name is Dave, I am building my second CNC router, which is of my own design. I based the design on my original cnc router, that I built from some plans bought from the internet. I am trying to improve accuracy and useability by buildin a heavier duty machine than the original

I have started building the z axis components and am having trouble boring the holes for the z axis rails accurately enough.

Here is a picture of the z axis so far




The curved component, which I am calling the motor housing holds the spindle motor (brushless DC) and is designed to move up and down on 2 parallel rails, which will pass through the rectangular z axis component and through bushes pressed into the back of the spindle housing.

I have tried to bore these holes in the mill once already, by clamping all of the parts together in a stack and drilling a pilot hole, then boring straight through.

The problem I encountered was 2 fold, caused I think by deflection of the boring bar, due to the long distance and small diameter of the holes. The bottom holes were slightly smaller than the top holes, which I fixed with a reamer and the holes were slightly out of parallel, which I couldn't fix and caused the spindle housing to be very stiff on it's rails.

I could have loosened the bushes a bit to overcome this, but I was concerned that the spindle would no longer be perfectly parallel and that I might introduce play, which I am trying to minimize.

I am hoping that someone will give me some tips about boring longish small diameter parallel holes

Thanks

Dave
Here's a picture of my workshop

[Kipper]

Nice looking design Dave!

I'd be inclined to machine that whole assembly as a collection of individual parts with a connecting block avoiding the need for the deep boring.

Although on my latest build I've flipped the part and realigned it to bore the other side.


I tend to make Oilite bushes a press fit and then ream them to size on the lathe....makes up for some inaccuracy too.

[DMBGO]

Thanks for the reply Kipper, sorry to seem ignorant, but what did you mean by a connecting block? Nice work btw.

[Kipper]

Thanks for the reply Kipper, sorry to seem ignorant, but what did you mean by a connecting block? Nice work btw.

In the attached picture I can't make out whether the blue item is a separate connecting block....My thought is to make the red items separate (I'm assuming you have either cnc or a DRO) and bolt the complete assy together.

[DMBGO]

Kipper, thanks again. Although the spindle housing is made from 3 pieces, it is loctited and bolted together, I just made it that way because I didn't have a big enough billet I dont have a DRO and my original CNC machine is too lightweight to do this. I have made these parts the old fashioned way. The problem is getting the holes in the spindle housing (Z axis) parallel with a set of holes in the rectangular y axis carriage, so that the rails dont bind.

[chich2]

Dave,
I have a Hafco HM-52 like yours that I converted to CNC Hafco Metal Master HM-52 CNC Conversion. Are you using the quill to feed down through the hole or are you raising the knee of the mill? It will make a HUGE difference on these machines as the quill run out is large. The further the quill stick out, the greater the run out. The tool always pushes away form the job therefore the hole you bore will always be tapered with a smaller dimeter at the bottom than at the top. I never use the quill on any machine to "bore" a hole because of this reason. I always lock the quill off firmly and raise the knee.

Hope this has been of some help,
Chich

[DMBGO]

Hi Chich2,
funny you should reply, I have read through your Hafco conversion thread a couple of times with great interest. I raised the knee rather than using the quill, your thread actually alerted me to this potential problem. I have been thinking about a similar mill conversion to yours, but I have to say I was a bit daunted by some of the issues you ran into, not least the movement at the base of the column! I went straight out and checked for cracks in the paint at the base of my mill when I read that, but so far mine is holding up. I have been considering all sorts of eccentric ideas to get my holes perfectly parallel, one of which is using some eccentric bushes in the top plate of the Y axis, so that I can use grub screws to adjust the parallelism of the rails and maintain a small tolerance in the bushes on the Z axis.
There must be a trick that will let me bore the holes dead straight and in line though....

[chich2]

Dave,
With the HM-52 you can also clamp the assembly straight down to your table, put your boring head into the horizontal spindle and use your "Y" axis to bore the hole. It has to be Parrell then! Don't forget to lock off the knee once you get it to the correct height and the quill and "X" axis before you start boring.

Yea my thread goes on and on and I will say I had a lot of fun doing it. BUT I would still REALLY like REAL CNC VMC one day!

Chich

[DMBGO]

That sounds good Chic, why didn't I think of that?
I will try to make time to set up and try it tomorrow. I will post the results in the evening.
I am sure that someone with your ability to follow a project through to the end, despite adversity, would eventually achieve a full VMC system
Thanks again Dave

[DMBGO]

I said earlier that I didn't have a DRO, but I do now! I had a 3 axis Easson one on order from China, but wasn't expecting it for a couple of weeks. The DRO left China last Thursday and arrived today, that's fast! The boxes look a bit battered, so here's hoping all is intact.
The DRO was half the price of the same unit from our local supplier. I purchased an extra scale, to fit to the quill, so I will have 4 scales on a 3 axis display and I plan to use a serial port switch to swich the readout between the quill and the knee.

I think I will start a new thread on the DRO installation just for fun.

I will put the new CNC router on hold while I install the DRO, it should make things a heck of a lot easier

[chich2]

Nice moove Dave! You will love the DRO. Be sure to post a link to the DRO fit out on this thread!

Chich

[DMBGO]

Hi again Chich, I've been busy in the shed with the mill, and work keeps interfering as well!
I've made a start on the DRO thread here
http://www.cnczone.com/forums/showth...559#post638559

Btw, how tight have you got your dovetails on the slides of your mill? I noticed when I had the dial guage on the DRO scale that winding the table handle was moving the X axis about 5 thou! I adjusted things up and now it's not sloppy at all, but I think it's probably too tight......