Re: Gantry 3-axis milling machine Design preparation phase
Hi Mogi - I have been thinking about how to machine the gantry and here's how Langmuir do it I think:
1) The gantry is fabricated and the top and bottom plates are 1-2mm thicker then needed as a machining allowance. Its stitched together not 100% welded which is wise. Plus the "flanges" created are useful for clamping edges
2) Then its sent to heat treat for stress relief. Now it can be machined in confidence its not going to move
3) The bottom surface is set up and faced to best fit and the perimeter is machined to create reference edges. Holes are drilled and tapped, bottom is complete
4) Its released turned over, clocked to edges & the top is machined - all good
Now you are going to get a cold rolled welded SHS so its a bit different unless you get it TSR - it will have lots of internal stress in it trying to change the tubes shape
1) Pick your best face of the SHS it will be crowned vs hollowed. This is the face to machine first (ideally you take this to a heat treater and TSR the SHS so you can move fwd in confidence)
2) you will clamp at the ends or hold in two big vices - half face the first face , release and check it out. Then clamp back and finish machine flat. Release and inspect. If it warps or bows stop here! if good Drill and thread all the bottom holes.
3) Decide which end is the reference end, machine square, machine a reference land the length of the SHS on one of the vertical sides
4) release and set up on the new reference face, use the reference end and the register land to clock the part. Now you know where all the bottom details are so you can machine the top in register
5) rough the top face, release the part and check, clamp back down, re-clock then finish machine
At this point if Venus has aligned and the machinist held his tongue right it will be flat and straight with no twist. If it has warped then you have a problem. If you can TSR the SHS its a very small cost compared to getting to this point and trying to recover the part.
A cold rolled and welded hollow section has quite a bit of internal stress in it and then you have to hold it somehow which will deflect it again. That's why you can't clamp it and machine in one go as the clamping deflection will be machined into the part....
Good luck - Peter
When machining large moulds in aluminium they are cut and released and rested several times through the process. Its quite interesting how much metal moves when machined and clamped.... The forum is full of "please help" threads using SHS or RHS and then the cars jam. Get the bearing manual and look up the manufactures specs for geometric tolerance of the rail lands and scare the machinist, Do the best you can with what you've got and fingers crossed :)
Re: Gantry 3-axis milling machine Design preparation phase
the solution to this is quite simple, do the surface by hand with sanding. no clamping involved, use a reference surface and go michealangelo on the steel. mark the reference with engineers blue and brush it onto the surface or mark the surface and brush with the reference. Machining shops can't be trusted unless they grind it too which will be more $$$ than the whole machine. patience by hand or $$$ by company or fail
Re: Gantry 3-axis milling machine Design preparation phase
Hi,
whether it can be ground flat is really determined by its length. There are plenty of surface grinders around but they start thinning out as the length goes up.
I'll bet there three or four in your area that can do 500mm length but may be only one that can do 1m. To my knowledge there is only one in the whole of New Zealand
than can do 4m.
The good news is that surface grinding is an easy task assuming you can find the right machine. Secondly if you get SHS it is typically pretty damned good anyway, seldom
would you have to remove 0.1mm to get it flat.
Craig
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Re: Gantry 3-axis milling machine Design preparation phase
Hi - It does not need grinding - milling is fine... the rail lands do need to be flat and parallel. Doing the surfaces by hand on both sides is unlikely to result in parallel surfaces... Craig Ozzies must make horrible sections, 1mm cup on a SHS is quite common. Mogi will need to hand pick his gantry section... Peter
The std allows for 0.8% concave or convex so for a 200mm SHS the max allowable is 1.6mm so beware! The straightness spec is 0.15% so over a 1500mm piece it could be 2.25mm bowed. Again beware!! but in general its much better than these... but don't rely on someone else to pick your piece! They will not care if its bruised, bent, twisted, fork lifted or hammered etc etc...
Re: Gantry 3-axis milling machine Design preparation phase
Hi,
agreed milling would be fine, although as it turns out grinding is cheaper...it takes but a few minutes to set up a grinder and then turn it on and come back an hour
late and its done. It takes longer to set up a mill and run it either manually or CNC.
I just ran a straight edge over my 100 x 100 x 9 SHS, and on any side any dishing or cupping must be less than 0.005 inch, its less than visually detectable.
So it may be that you Ozzies are a bit slack when makes RHS....mind you with all the hot air you guys spout I doubt anything needs thermal stress relief off the mill!!:)
Craig
Re: Gantry 3-axis milling machine Design preparation phase
Yeh I agree 6 of us can heat treat something over morning tea sometimes. :) Peter
Re: Gantry 3-axis milling machine Design preparation phase
Hi,
I notice that the UN has issued a cease and desist order against both the Kiwi and Ozzie parliments on the basis of hot air they produce, the climate effect must be untold!
Craig
Re: Gantry 3-axis milling machine Design preparation phase
Hi Mogi - Excellent seems you have all bases covered so making good steel parts no problem. Keep at it. Peter Oh since you have access to HT I suggest you design all your parts then make them all and have them TSR in one hit. It will be cheaper then in a few goes. Peter
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Re: Gantry 3-axis milling machine Design preparation phase
Hi Mogi - Here's an axle I designed coming out of heat treat. Its at 650C its for what we would call a small trailer (250T). I have done much larger ones...So your parts will be a nice cherry red. Craig it took 25 engineers, 16 politicians and the receptionist 2hrs of hot chat to get this preheated... Peter
Re: Gantry 3-axis milling machine Design preparation phase
Hi Mogi - You are building from mild steel. Mild steel does not change strength if heated to red then let cooled. In the axle case this is a CrMo steel being heated then quenched. After quenching it will be very very strong but brittle. So then it is tempered to the required strength and toughness. The axle is heat treated to 1400MPa UTS. Mild steel will be 250-350-450Mpa yeild.
Now we need to discuss concrete. Why do you want to use concrete? Two main reasons 1) to add mass. Steel is 4x denser and 7x stiffer then concrete and cheaper so add steel if you want to add mass 2) Its damper? well the machine base rarely vibrates so why add a damp material to the base? The Z axis and saddle are the main culprits in the damping/vibration area so they need attention not the base and a 3rd reason is this machine is going to be wet with lubricant. It will get everywhere and it will seep down the joints between the concrete and steel and 2-3 years or less the concrete will be a separate mass to the machine and be pointless & be a problem. I strongly suggest you stay in the steel universe. Unless you want to cast a machine base and thats totally fine.
Then you will have to seriously consider swarf and what do you want to make with this machine? A good machine is tailored to its purpose. A general purpose machine is always compromised in some way. If your only going to make small parts then a big gantry machine does not make sense etc. So this machine is going to make huge amounts of steel or aluminium swarf which will be a problem. Look at commercial machines and decide if you are going to make a swarf tray. ie there will be a table with slots each side and the swarf falls into a tray. This cannot be done if you make a closed machine base and you will have to shovel swarf out into garbage bins. Its better to solve all of these things at the design stage rather then down the track. Your options are good at the design stage poor once you start making things... The enclosure, swarf and lub system need to be thought thru. Peter
Re: Gantry 3-axis milling machine Design preparation phase
Hi,
I thought I did a good job of pre-planning the enclosure....but I failed.....miserably.
Its still a vast improvement over my first mini-mill but I thought with this design I was going to able to splash coolant around with impunity.
I've come to the conclusion its easier to design and build a boat to be waterproof, ie exclude water ingress than it is to design a machine that
can contain its own coolant!
Oh yeah, swarf builds up always in the most inaccessible corners, that is after all swarf's main purpose in life.
Craig
Re: Gantry 3-axis milling machine Design preparation phase
Quote:
Originally Posted by
peteeng
Now we need to discuss concrete. Why do you want to use concrete? Two main reasons 1) to add mass. Steel is 4x denser and 7x stiffer then concrete and cheaper so add steel if you want to add mass 2) Its damper? well the machine base rarely vibrates so why add a damp material to the base? The Z axis and saddle are the main culprits in the damping/vibration area so they need attention not the base and a 3rd reason is this machine is going to be wet with lubricant. It will get everywhere and it will seep down the joints between the concrete and steel and 2-3 years or less the concrete will be a separate mass to the machine and be pointless & be a problem. I strongly suggest you stay in the steel universe. Unless you want to cast a machine base and thats totally fine.
Then you will have to seriously consider swarf and what do you want to make with this machine? A good machine is tailored to its purpose. A general purpose machine is always compromised in some way. If your only going to make small parts then a big gantry machine does not make sense etc. So this machine is going to make huge amounts of steel or aluminium swarf which will be a problem. Look at commercial machines and decide if you are going to make a swarf tray. ie there will be a table with slots each side and the swarf falls into a tray. This cannot be done if you make a closed machine base and you will have to shovel swarf out into garbage bins. Its better to solve all of these things at the design stage rather then down the track. Your options are good at the design stage poor once you start making things... The enclosure, swarf and lub system need to be thought thru. Peter
Hi peter,
About why i wanna use Concrete, langmuir used it, and since i'm copying their design so i'm going with it and here is the reasons why it make sense to me.
1. Concrete in my country is way to cheap how i calculated concrete will add about 400kg to the machine base which will cost about 50$ if i wanna add that kg of steel it will cost 500$
2. Already i will have a steel plate planted inside the concrete that will be the bolting surface for the vises it will weigh about 80kg
3. above concert will be epoxy layer to cover it from the elements and to create a coolant flowing surface
You can see the assembly of Mr-1 here https://www.langmuirsystems.com/mr1/assembly
Re: Gantry 3-axis milling machine Design preparation phase
I don't know why people insist on flood coolant, truth be told only high performance metals need flood coolant and you definitely won't be cutting those. Aluminium can be dry machined or if you must insist use mist coolant, just enough to cool, not enough to pool, ideally something that evaporates each night, though compressed air will work just fine, all you need to ensure is chips aren't being recut after all.
Complicating builds with features that aren't needed is number 1 mistake, almost as bad as using leveling epoxy under the rails.
Your concrete has to be non shrink grout, otherwise it's pointless. Copying a poor design is inadvisable.
Re: Gantry 3-axis milling machine Design preparation phase
Hi,
Flood coolant results in vastly better tool life. Its also best on plastics where you absolutely must get the chips out of the cutzone or the chips weld themselves back together.
You machine your stuff which ever way you want and I'll machine my stuff the way I want which includes flood cooling....and I won't be asking your permission!
Craig
Re: Gantry 3-axis milling machine Design preparation phase
Hi Mogi - So you want an extremely heavy machine? The mass is great argument I don't agree with. But set a course and in a couple of weeks or a couple of years you will find out if its the right one. 400kg of concrete for no good reason is strange to me. Think about this. The concrete is not in the loadpath from tool to structure. The loadpath goes thru the steel bed to the bolts holding it to the frame which is all steel. Steel is 200GPa stiffness and concrete is 40GPa so the load travel's thru the stiffest medium which is the steel. So the concrete just adds weight. So sensible design of the base in steel will be better. If concrete is cheap then make a cast machine base in concrete then you have a damper, potentially stiffer lighter structure then a space frame. Then extend that to a cast gantry....But do some FE to sort that out.
Plus concrete and steel have a bond strength in the order of <1.0MPa so I believe its a never bond situation. That's a strong reason LM have gone to EG in my view. Epoxy is known to stick to steel really well... Peter
