Here we go again . . . MK4

[routercnc]

I managed to finish off the remote grease extensions. The threads were tied up so the grease nipples now sit flush on the end of the tubes:


Then machined 2 flats (8mm AF) which were aligned to the flats on the grease nipple. This is to allow the tubes be inserted after the bearings are fitted, making it easy to fit/remove the Z axis - something which might happen quite a lot when setting the machine up:


Here they are complete:


The single straight one (left side) is to service the lower bearings and is fitted to each unit as required, then removed.

Then onto the Z axis. These are the large side pieces, each 30mm thick. I'm machining them as a pair to get whilst I get them to size. Outer dimensions on most edges are critical as they will hold a pair of Z axis rails and need to be parallel, true, and hold a tolerance on the dimension.

They are too wide to go on their side on the bed or vice, and too thick to sit flat on the bed, so had to set them up on the edge:


Dialled them in roughly to avoid having to machine too much material away


Tops machined flat - left a tiny bit next to the vice which I filed away by hand:


As the parts were too thick to machine the ends, I marked a datum on the left end (+0.5mm longer than final dimension), and one on the right end.


Then set up a parallel edge. This was so I could flip the parts over and rest the machined edge against this. Took a long time to set it all up and be sure it was good, but them machined the other side.


I was pretty relieved to get to this point with both edges parallel and part to size (96 mm). However what I didn't know at this point was that this new top surface was actually on an angle and it was more like 95.7 mm (!) on the other side. Don't know if the fixture slipped during machining or what. But it is out by way too much for the linear rails.
I think my recovery plan will be to re-machine both parts to 95 mm (1.0mm underside) , and then use machine epoxy behind one set of bearing carriages to fill in the ~1.0mm gap. This might turn out to be a blessing in disguise as this will ensure perfect alignment.

Then onto drilling and tapping the holes. Not much to report here, standard stuff tapped to M5. But I did make this tap guide from a bit of aluminium round. The last part of the hole is tapped to M5, then there is a 6mm clearance. This guides the tap into the thread perfectly. Might make so more for other sizes:



I didn't get a picture of the last ops but I basically machined the ends to final size using the datums machined on an earlier op. I had to flip the part to do both sides.

Once I sort out the edge machining problem, there are some straightforward holes / counterbores to come, then I need to figure out how to machine some detailed features onto the ends. I think I will cut a hole in the table the machine sits on and poke most of it through into the draw space underneath.
The final op after that is to drill an 18mm clearance hole about 200mm long through the centre of the part (ballscrew sits inside). I think I'll do that on the lathe . . . bit more thought required.

[Lee Roberts]

Looking great and coming along nicely!

[routercnc]

Looking great and coming along nicely!

Cheers Lee.

If I get a chance I'll post up a more detailed set of measurements and photos of the long side parts I'm making. Having measured them on my 'surface plate' they are out by more than I thought so I've spent the last few days working out what to do, including starting them again.
They need to be accurately made because they take linear rails on both sides.

Current plan is to use the lathe to square up the parts. I've got a couple of fly cutters on order which will go in the chuck, then I need to make a raised platform which sits on the cross slide (toolpost removed) which will hold the work. I'll then feed they work by winding the crossslide past the chuck and square up the edge. I have a ground straight edge which will sit behind the other edge of the path so when it is flipped over the freshly machined edge will sit against it and mean that the second edge will be parallel to the first.
Only problem is that the cross slide had about 110mm travel and the edge is 310mm long so I will need to index it along the ground reference edge 3 times. Will this give an accurate long edge or will it give an edge with 3 facets? I will find out !

Anyone with a better idea as it won't start work on the raise platform until the weekend ?

[routercnc]

OK here are the detailed measurements showing how far off 96mm width the parts were (!). I think they slipped / tipped in the fixture, which I couldn't tell as I couldn't see the ref surface they were sitting on during the machining.



They are out along the length, and across the width. Annoying but there we go.

Current plan is to machine them square again (but obviously they will be undersize for width). Here is a sketch of what I'm thinking of attempting on the lathe:


I've bought some 5mm thick aluminium strips which I will superglue and bolt to one of the edges using countersunk cap screws, setting them well underflush. Then I'll machine the edge back to get the part 96mm wide, using the lathe again, and then remove all of the screws (except the ones at the far ends which will hold the strip on, along with the glue). I can then attach the rail. Should look like this if all goes well:


If it doesn't work then the strip can come off and I'll try something else. Thought about epoxy levelling all 4 surfaces, which I think can be done if I start on a level surface and do it in the right order so they all end up parallel to each other.

Another option is to do both sides but use steel strips instead. Then get them ground in pairs on a surface grinder so they are parallel and flat to each other.

I knew this bit was going to be challenging, but it must be right otherwise it will bind or not track straight up and down.

[routercnc]

Progress has been slow because this has turned out to be more involved than planned.

I started by making a raised platform for the lathe. This was to hold the part whilst I used a flycutter to trim and true up the long edges, ready to take the add-on strips. Here are the long T-nuts being made:

Started with the drawing and some stock:


Machined to size:


Finished:


Trial fit in the cross slide, plus made up some simple spacer tubes:


The top plate (a large offcut) was bolted and shimmed using shim stock on the spacer tubes until it was as flat as possible:




Then a straight edge was dialled in:


Edge skimmed back:


Glued and countersunk screws used to add the extra strip:


Ready to try again, this time a different set up which shouldn't move!


Skimmed it all down to 96 mm trying to get within 96.00 - 96.05 everywhere. I used the height gauge to check progress and wrote the heights on the part. Here is it getting close.


I also left a machined edge on one of the sides for the rail to align to.






Hopefully that will be good enough for the rails to run on.

Machined the counterbored holes:


Ready for the end features . . .

[routercnc]

The part was too long for the machine so only one thing for it - cut a hole in the table:


The profile pieces which make up the bed are not accurate enough to be used as a support. The sides are not flat and are not perfectly square to the bed (since that was skimmed by the machine). So I made up a 'tramming' plate:


I bolted it at the bottom, then used a screw at the top to dial it in. Here you can see that before the screw starts to be tightened there is an uneven gap to the part I am machining (which is held at 90 degrees to the bed via the precision vice:


Screw tightened until it made contact:


I made up a strap clamp to hold the part and bolted it to the tram plate. Then it was ready to dial in by running the indicator up the side and adjusting until it was vertical:


Then the features were machined:


Took the part off and put it on the lathe, then used a centre drill (as a scribe) to mark along the edge (part not shown in photo):


Then removed it and used the height gauge at 15mm (part is 30mm thick) to scribe a line. I was relieved to see it was exactly the same height as when on the lathe which meant they were both at the same point.


Basically this meant I had got the lathe platform at exactly the right height, with the centre of the chuck in line with the centre of the part. The next op on the lathe is to drill an 18 mm clearance hole (for the ballscrew) about 190 mm deep into the part.

But that is on hold until I machine the end of the second part. Before I took the first part out I had added a backstop to pickup the edge. This meant it was in the right position. Here is the second part set up for the same end machining:


Getting closer now but this bit is taking ages . . .!

[Zeeflyboy]

Well you are certainly putting in the attention to detail - hopefully it pays off in the end with a nice and smooth machine.

Good to share your techniques too, always interested in how people approach certain problems or use equipment in creative ways.