Reasonably Rigid Router (RRR) - a cautionary tale (likely) in the making.

[peteeng]

Hi Luke- tell the Heat treaters that time is not a problem and your happy to wait for your job to be included with another. That should bring the price down. Peter

[luke peter]

All good points Peter. It makes sense to have the mech side of the machine as glose to good as I can reasonably get it, because it will be the most mission to modify after all is said and done.

I imagine qc on bent sheet metal parts must be pretty stringent, lots of opportunity for error. I assume the guide mount surfaces are machined post bending also?

[peteeng]

Hi Luke - At the price point the machine sells at there is no room for post machining so no, all parts are off the press. I have moved some parts to billet machined to remove some heartache out of the parts and assembly. The QC at the sheet metal shop I use is really good. I have tried several shops and have come back to them. They were across a closed border the last 1.5 years which made life tough but now its reopened and I can get back to "normal" suppliers & routine.... Peter

[luke peter]

International Covid insanity neatly tripled the cost of shipping from china vs 2 years ago, I can appreciated that Australia's border restrictions must have been onerous (I started the process of trying to immigrate there just before covid happened, and have not progressed much).

Do you use linear profile rails on your builds? Their mounting conditions are fairly stringent, and I haven't come across any sheet product (aside from Mic-6 plate perhaps) that satisfies that flatness requirement. Though I imagine it will be less of an issue if the structure they are mounted on is relatively flexible (which would be the case in a hobbyist maker intended machine).

[peteeng]

Hi Luke - I use 20mm square rail on all builds, house brand BST Motion https://bstmotion.aliexpress.com/store/314742 medium preload . They have been very good. I've used chinese, korean and japanese bearings all good at their price points. I'm about to use some round rail on a build to get a feel for them. First machine buyers don't know the difference and they are a big $$$ difference and for the typical first buyers I get they will be fine and they make $$$ decisions not performance decisions.

Yes freight has killed a few sales lately and I have friends that have not been back to family in europe for over 2 years... been tough for some, one friend has not seen his wife in 2 years!! ... Peter

[luke peter]

Welded the risers onto the gantry box this morning. The horizontal flat welds went perfectly, the inside corner fillets not so much... I don't do consistent enough projects for me to retain competency apparently. I am going to dig in the scrap bin and run a bunch of practice fillets until I am certain I am not going to ruin good material.

I did achieve a measure of success after bumping the current 15% up from my flat butt's... Hopefully I can regain some consistency after an hour or so of practice.

[luke peter]

It turns out current was the issue, my little inverter likes 118A for fillets with 3.15mm electrodes (at least with the 6mm scrap plate I was using to practice). I got 15l of vinegar for a soak preparation of the small parts (to strip mill scale and any residual rust). I hope to have the gantry complete and ready for stress relieving by the end of the week. Then onto the x axis rail supports...

[luke peter]

Update time...

But first - some cautionary information:
If you decide to tidy your garage in flip flops, and then decide to do a spot of welding, you will burn your feet with spatter and flux (I learned this for the 50th time today)
Do not be too eager to remove flux to see your wonderful weld bead, it's probably not wonderful, and if you don't wait for it to cool, it can pop off and burn your eye...

My garage got to the point where the relics of too many processes were lying around, so it was cleanup time. I got a new (to me) pedestal drill that I am extremely happy with, it will make the rest of this build considerably more manageable with its glorious 25mm drilling capacity (my little press struggled with 12mm, its motor is tired) and its chunky cast table - most importantly, it was cheap. My little makers corner pictured below:


My fillets have improved dramatically, to the point where I would consider them "good enough" to continue the build, with minimal cleanup required compared to my disastrous earlier attempts. They are still very far from great, but I believe they will be structurally sound for this build. This is the first rail support bar being attached to the gantry box (1 full length fillet, one full length butt)


Butt weld on same rail support:


I am pretty happy with how things are progressing. The gantry riser plates are very close to perfectly orthogonal with the rail support bar, so hopefully I will minimise the amount of material that must be removed during machining.

[luke peter]

Update.

Gantry fabrication is finished. Both rail bars are on, and my welding is OK now. I am a little concerned that the top rail (gusset supported) will be the weakest part of the gantry, but it was designed for a specific bearing spacing, and the c channel I got wasnt wide enough - hence the extension.

I managed to complete all these welds without burning myself, not even with UV - there's some growth for you...
face and sides

gusset fillets

back view


I am happy with how I have managed to fabricate this chunk of steel. I burned about 3kg of electrodes, and my welds improved a lot during the process.
There is still a lot to do, but at this stage the only barrier for a good long while is how much time I need to do it.

Ta for looking,

[luke peter]

I am revising RRR's name, its a mouthful. Henceforth, the router formerly known as RRR shall be called Steve.

[luke peter]

For posterity:

Using scrap for projects saves a lot of money, but the time cost is proportionally high. I spent close to 2 hours yesterday just stripping rust and paint from the two lengths of channel I am going to use for the X rails supports, and dimensional issues have to be carefully considered with space left for adjustment before final fit-up. I do not, yet, regret using re-purposed steel, but for others who may be considering it, if time is a significant constraint, build with fresh material.

Aside from the time, it is a messy process that covers my garage in dust. I do not enjoy it.

[luke peter]

Some progress... I was away last weekend, so nothing real completed in my spare time.

When I returned, I did some prep and started welding the X axis rail support beams. At this point my welder decided it was time to give up. Two capacitors on the mosfet driver board badly burned, hopefully a simple swapout - I will see once the spares arrive.


I took the opportunity to start on flat stock preparation, drilling the holes that were too small for the thickness of plate I was cutting etc. I completed the z interface blocks, I will grind them to thickness tomorrow.


Drilling and countersinking is actually remarkably time consuming - in your head its a quick 20 minute thing, but those 4 plates took me the better part of 1,5hrs to punch, centre drill, drill to size, and countersink.

[luke peter]

FFS, I was checking model thickness of these plates to see if I had any meat to grind them down a bit, I dont, but also - I cut 4 of the bottom spacers, and none of the top ones...

Measure twice, cut once - when will I learn???

[luke peter]

Replaced the damaged capacitors, there was space for 3, and it looks like there may have been three there originally (I could only see the remains of two).



Strikes arcs again as before, so R100 for spares, vs R2000 for a new welder. I am OK with that.

[luke peter]

I noticed some surface separation in my model of the gantry beam... For some reason Inventor didn't recognise the mating faces of the channel - so I removed the fillets on the edges and added a 3mm weld seam. I also modeled it with a remote load rather than the "stiff" Z axis.

The results were significantly better in terms of stiffness... 20800N/mm (20.8N/um) to 170000N/mm (170N/um).


This was the weakest part of the assembly before, which was counter intuitive to me considering how beefy it is, and its all steel construction. This model actually makes more sense. I guess I wont know how it will turn out until I actually load the gantry with indicators, but I really do think this model is more representative.

[luke peter]

I installed the x axis rail bulkheads today, Just the bearing plates/motor mounts to do, and general cleanup, before they are ready for machining. I am going to use the ball screw assemblies to setup the bearing plate positions, with a 2mm offset to account for the depth of the intended rail slots.

[peteeng]

Hi LP - Steve that's funny! I worked in a Eng Ofice once and anything whiteout a name was called Steve. Steve will be fine. Peter

[luke peter]

Sigh.

I changed the loading to be in the y direction of the machine and ran some x+y FEA. The results are unappealing. For some unknown reason, I didnt load the assembly sideways when I was doing my square tube assembly, and likewise didnt do so with this assembly. I specifically disregarded lateral triangulation on the outsides of the x rails because I was under the impression they were not required.

The image below tells another story... When the loading is switched from x direction to y direction, the stiffness is almost an order of magnitude less... (160N/um vs 37N/um). I dont really have space to stiffen this axis also...


The relative difference in x stiffness vs y stiffness is about 40%. Suggestions?

[luke peter]

Simple jig I used to keep the upright plates coplanar and consistently spaced for tacking.




Hopefully a measure of accuracy in the weldment will cut down on machining later. I am also considering using epoxy surface replication instead of machining on these components (the uprights onto which the X rail beams will be bolted). It will come down to costs at the end of the day.

[routalot]

The obvious solution to the deflection would seem to be extending the base sections outward by an amount and adding webs to triangulate the location of the rails.A rugged job on one side might be enough.I hope everybody building a machine follows this build as some of the proposals that appear here are much less structurally sound than this one,which does recognise that deflection doesn't only occur along the machine.