Here we go again . . . MK4

[Davek0974]

Twin ballscrews on the Z - should be able to punch the cutter through the work with the motor turned off !

:)

[njhussey]

Nice looking clamps! I'm about to change the way I cut the kits for eBay, instead of using masking tape to hold them down on the bed I'm going to cut out the 915mm x 102mm (by whatever depth the balsa is, 1.6 & 2.4mm) out of a piece of MDF and then using a cutter twice the diameter I normally use (2mm in this case) rout out 1mm deep the programming so that when I cut the wing ribs or fuselage sides I can send the cutter up to 1mm below the wood to ensure I cut all the way through. I'll be making holding clamps (sorry about all the waffle to lead up to the clamps I'm going to be making!!!) the same shape as single servo horns which I can swivel over the balsa to hold it...going to use some scrap 4mm Ali I've got lying around...hope that makes sense? :)

[routercnc]

Hi Neil,

If you mean using a spoil board then I'd agree that is a better way and one that I use as well for balsa/liteply.

[Lee Roberts]

Sorry to read about the problems, all part of the fun...I think? Lol

On a positive note, you've got this as the money shot though a:



They look nice and look to be doing the job just right too, nice job

.Me

[routercnc]

Update time. It soaked up many hours to get back on track. After a lot of prodding with any pointy shaped tool I could find, plus a soak in WD40, I manage to lever the broken spot drill out of the hole. The edge of the hole was a bit damaged where I'd levered against it but at least the hole was clear.

After checking the main part of the hole was still in alignment I bored it out from the 6mm spot size to the 6.8mm pilot, then ran the M8 tap into it. I had to give it a generous countersink to tidy up the damaged surface then all was well again.


I also managed to drill and tap out all the holes in the bottom of the outer edge from dia8 (should have been 6.8 for an M8!) to pilot 8.5 and then used my new M10 spiral flute tap. As per my recent M8 tap this is also a RotoGrip tap and is very sharp and cuts really well. This one was £11.03, which sounds a lot vs the cheap ones but I think it is worth it having used both.

Here is the ebay link:
http://www.ebay.co.uk/itm/2917546426...%3AMEBIDX%3AIT
In case the link expires in the future here is the description:
HSS Ground Machine Tap Spiral Flute M10 x 1.5 Quality Made by Volkel. Germany


The button head M10 cap heads had also arrived so I was able to trial fit those. All looking good:


Next job was to cut the RHS steel beams to size. I was going to mark it out and use the thin grinding wheel on the grinder to cut it but after lots of deliberation decided it was time for a new tool. In the end I went for this one which is the 355mm rage2 saw. This is because it can cut up to 120mm x 120mm which should cover all needs. It has a nice soft start and just drops through the steel with ease. It is also pretty square out of the box - helped by just having a pivot and no slides etc.


The first beam was cut out and offered up. Looks OK. It is about 0.5mm short of the 730mm length as drawn to make sure I could set the end pieces the exact distance apart.



Next I need to cut the 2nd beam to length then I'm thinking about the best way to set the ends the correct distance apart. Current thoughts are to maybe use the CNC machine to drill out the holes at each end in the side of the RHS beam, including a special hole for a hardened dowel locator pin at the far end. There would be a matching locator hole in the triangular brace side plate at the far end to push the dowel through. This should set the far end housing a set distance from the near end housing.

Another option, is to CNC machine 2 shallow pockets into a large sheet of plywood to take the 'footprint' of each end housing and set them the correct distance apart plus have them squared relative to each other. I could just use a tape measure and square but feel like an assembly jig / guide would be nice. Any other thoughts?

[njhussey]

That's looking good now, coming along nicely! Sad I know....but I do like to see lots of shiny metal with lots of holes drilled in....note to self, must get out more

[routercnc]

Second beam cut to length using the first beam as a guide:


Decided to use the CNC machine to drill the holes. Here is one of the beams clamped down and being dialled in. Obviously the edge is not very straight but I wanted to get it fairly close:


6 holes at each end drilled and then milled to 6.8mm, plus a 6mm dowel pin hole at the far end:


Then onto the tapping to M8:

Yes I know, ended up with holes a bit close to the edge - they were covered by another part in CAD and did not realised I put them so close to the edge. Will still work, but could have been better.

Then a trial fit. Note that only the front beam has holes in, and these are only in one side. Still lots to do on these bits. It all fits and aligns well but as I suspected would happen when the bolts are tightened it lifts/rotates one end of the gantry about 0.5mm from the flat plane. This is because the RHS is not perfectly flat along the lengths and so the ends are forced to align with the sides of the RHS.


I intend to machine just enough on each edge of each face to get it all square. This could be just the outer 3-6mm or so as I'm hoping the raised bits are on the edge / corners so just knocking these back a bit will create surfaces which are in plane with each other and square. I think that when I tighten the bolts the membrane flat parts will pull up tight to these new surfaces on each edge and everything will be square again.
I don't want to machine to whole surface as this will make the part quite a bit smaller. We'll see how it goes and then I'll repeat on the other one. Maybe should have done this before the holes . . .
but until it was pulled up tight I didnt know how much it would move.

Anyway then I'll take off the triangular corner plate at the far end and machine in a matching dowel pin hole which will allow me to get the ends the right distance apart from each other.

Actually on this note I noticed that the 6mm end mill I used to drill the 6mm dowel pin hole in the RHS actually made a slightly larger hole. Putting a 6mm shank in there showed it to be a loose fit. I suspect the runout in the chinese spindle may be adding 0.05mm all round so 0.1mm larger diameter? If so I'll use a smaller end mill and interpolate the hole but creep up on the fit.

[Clive S]

Looking very nice ad sturdy.

This is how I got my beams sorted I welded 15mm plates on each end and then had them machined parallel and to length. I also had two faces of the box machined to get the box section true so that the front plate could be bolted to the beams true.

[Lee Roberts]

Looking good, good luck with the next beam!

.Me

[routercnc]

Well I haven't moved onto the 2nd beam yet for 2 reasons. Firstly I've decided to do all the work on the first beam and make sure it is all going to work out. Secondly, although the outer face is now machined flat, I realised that the lower face is not flat enough. So I started by machining that square to the outer face (part is upside down):



It now sits properly on the base plate and is square to the outer surface:


I then flipped it over and spotted all the rail fixing holes in the top surface for the rail.

Next up was to add the reinforcement plate on the inside. I chopped 2 bits to length using the new Rage saw - really easy and quick:


I used metal epoxy to glue the strip in having first sanded and de-greased both surfaces. I then knocked them both with my knuckle and the epoxied strip one doesn't ring like the other beam. Although I'd added this strip to give reinforcement and extra depth to the rail bolts it has also helped with the resonance. Might help with the cut finish a bit:


Then opened out the small spots made on the cnc machine and then drilled and tapped the rail mounting holes to M5:



I haven't machined this top surface yet as I will do it as a pair with the rear beam to get them exactly the same. Although they will have 5mm deep epoxy on top to mount the rails on, and therefore don't need to be machined, the 'MDF mould' I'm drawing to pour the epoxy into needs to sit on a very flat surface. I'll show more when I've finished the design of this mould part.

Then a trial fit and it sits squarely on the base plate too now:




There is another bolt to go inside on the lower face, plus 2 holes to drill in the inner vertical face to add another connecting block. Basically the RHS will be supported on all 4 sides so should be a pretty good joint when done. Then the end plate will go back on with the stepper mount in.

Finally, something I wondered about recently. All the spot drills I've bought and used have been 90 degrees. The twist drill is 118 degs so when it goes into the hole it contacts only a 2 points until it gets going which is a bit hard on the drill cutting edges. Centre drills are 60 degrees so same problem. I had a look specifically for 118 deg spot drills on ebay and they only came up on the american ebay site and there weren't that many. I didn't look for long so could be me but are the 118 deg spot drills not popular? Or are 90 deg spot drills designed to give good centering alignment on 118 deg drills?