Here we go again . . . MK4

[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.

[routercnc]

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.

Thanks Zeeflyboy. I hope it is smooth, especially the Z axis which needs to be accurate and aligned so that the 4 rails don't bind up.

Some more progress on the long side parts of the Z axis. I finished the end machining on the other side piece:


Then it was over to the lathe to bore the 18mm clearance hole for the ballscrew to go inside. Here is the first one set up and a pilot hole being started at the bottom of the large counterbore:


Worked my way up using larger drills and then removed the chuck and dropped in the final 18mm bit. This has a 2MT on the end so needed MT3-2 and MT4-3 adapters to fit in the MT4 headstock taper:


This went OK but I ran out of travel on the carriage so needed to re-position the work closer to the headstock end. By doing this the 2 'tabs' on the end of the work (which were to stop it sliding under the pressure of the drilling) couldn't be used, so I ran without. I noticed after a while that the work had moved on me ! - so, I drilled and tapped some holes and mounted it directly to the plate, using the strap clamp I'd made earlier. This was much better. You'd think I'd have learnt by now that clamps can't hold work pieces and stop them sliding if the tool pressure is high.


I had originally intended to bore from one end and make it a blind hole. But the drill was not long enough and although I could have bought a longer one I decided it was just as easy to drill from the other side and go right through. I'd just put a nice blanking cap on the bottom to stop the chips going up inside and landing on the ballscrew (it is right next to spindle where the chips will be flying around).

Problem with that was that the drill bit was not quite long enough and left a small ring of aluminium where the 2 holes met (the blank ring about half way down the hole):


I managed the clean it out with my longest a round file and all was well. Repeated on the other part and big holes finished. I checked the ballscrews and they fit without touching the sides.

There is one small tapped hole to put in each of these parts, plus the blanking cap, and then they are done.

________

Spindle Block
Had a great surprise recently. The spindle mounting blank was too large to fit on my machine so I'd called in a favour from someone with a bridgeport sized / type CNC machine. I only asked him if he could machine it to size, then I would do the rest including somehow doing the 80mm bore in the middle. To my delight he gave me this back:




I couldn't have done that on my machine so I was very pleased to say the least! Now it still needs lots of M12 holes drilled and tapped in the side, some M8 in the front (for the clamps), and the bore is at 79 mm, so needs opening out to final size but that has really given me a head start on it.

The M8 and M12 holes are easy to do, just setting up time etc. The bore will need to be done by putting the part on the lathe cross slide and then I'll need to make up a line boring bar which will run between centres using a dog drive off a drive plate. I've seen this done but not done it myself so I might do a practice piece first.

Couldn't resist a quick dry fit just to check it was going to fit together:


edit - just noticed the spindle block is upside down in the photo ! I'll make sure to turn it around before machining the mounting holes in the side.