Originally Posted by
wildwestpat
Hi Khalid
This will be a monster of a router and is heading to be a verical mill or bridge mill as suggested by Dick Z.
1. The weight of the cast iron table will exceed 400kg (900 lbs) and possibly treble this ias you intend to have 'T' slots let into the top surface of the bed. The bed will require a careful design of strengthening webs on its under side to give adequate stability - look to the design of a cast iron surface plate of that size to give you the sort of cross bracing and webs that are required. Initial machining would be a difficult to do on the actual machine due to the tough nature of the outer skin on a sand cast iron item.
Ans: I totally agreed with you and no doubt I have in mind to make a Truss-support structure for holding the heavy top bed plate..I was thinking that i will level the Top plate with the Router itself, but Now I will see some more ways to reduce the misalignments and inacuracies in the bedplate so that minimal DOC require for the router to surface the Bed... I think of using Cast Iron bed for vibration dampning..can i use ordinary thick Steel plate as bed... As far as T-slots are concerned, We can have some alternate ways to hold the Work Piece...
2. This is going to be a tough order to maintain over 60 inches. Look at the ballscrew specs and be prepared for the price as these will have to be large diameter. The use of servo motors and linear glass scales would be a better approach and you could then use a less highly specified ball screw as the absolute accuracy is provided by the glass scale.
Ans: Tomorrow i will raise PRICE ENQUIRY for 6ft 1" dia ball screw, and will see the actual price... However as per your advice I will also study on the servo and linear glass scales as i am newer to servo things... I will make the drawings of the machine and will share with all of you... I am Incharge of big Machine shop( Later i will disclose the capabilities of the machines i have)...
3. Yes but to get the necessary ridgidity over the 60 inch span of the bridge will entail a very robust and hence heavy assembly. You should be thinking box ways not simple slide rails although the total weight of the bridge will help to dampen any tendency for the bridge to tilt under the infulence of cutting forces.
Ans: Agreed with You on this... The first day i have in mind to get the accuracy the machine should be heavy weight, rigid and carfully designed... The most important for me is the design of Z-axis... It should be very rigid and accurate... Again In the Drawings I will show you the sizes and thickness of H-beams, C-channels, Angle Irons that will make the Gantry...I have doubt on the vibration dampening capabilities of structure steel.. So i have to make some concrete pouring arrangments or other ways as per yours suggestions...
4. Same observations as under 2 for accuracy use glass scales as the feed back element in a servo system as this will be cheaper and much better than using precision ball screws.
Ans: I will Look into it... Thanks for guiding me...Currently I have 1200 Oz-in 4amp/phase 80V Stepper Motors....The servos will be in my secondery List, If i failed in stepper i will definitly look for servo system...
5. I sense that this is not the right approach. Identify the cutter you will be using and from there obtain the speed and power required. Mild steel in thin section is nasty stuff to machine if you are going to rely on 'T' slots and clamps to hold the work down. Much better to thing along the lines of double sided tape and a sacrificial ply or mdf backing plate that is screwed at frequent intervals to the bed. A magnetic chuck would be the ideal but one hell of a device if you must take a 60 inch square sheet at one go. Why not chop the sheet up first and make the mill that bit smaller.
Ans: Yes You are right, I gave the 20IPM and DOC values as the Minimum the machine should able to do... I know the Feed, DOC depends on many parameters i.e. Spindle Speed, No of Flutes, Material of cutter, Size/Dia of cutter, Cutting Fluid etc...
I use Double sided tape on my wood router... I never saw double sided tape and MDF backing plate on any metal cutting machines.. Do they have power to hold the workpiece combating heavy cutting forces and cutting fluids?...
Hmmm.. some time we have Tube sheets upto 5feet in diameter.. On which we have to machining and later drilling operations.. Currently the drilling operation is manually and very hectec... We have three radial drill machines and currently we are doing drilling of baffles plates each 20mm thick (Material is Low Alloy Steel A182 F22 or equivalent) Almost Eight plates are tack-weld and then they go through drilling operations ( 19.05mm final hole dia)... So we change the drills sizes more than 5-times to get the final size...
This is the reason I want to make the working area 5ft x 5ft.. I know the smaller the working area the rigid the machine and less complex design...
6. I have responded in 1 as this is linked to the size weight issue. The use of 'T' slots I have questioned in my response to 5 as mild steel in thin section and under high feed rates can pickup on the work. You will need to think of both swarf removal and adequate cooling and lubrication of the cutting tool. As mentioned under 5 above.
Ans: You are 100% right... But Once the workpiece hold with the clamp in T-slots...The machining operation started , then all the T-slots will strted filling with chips and may be the chip removal will be difficult.. I need your advice and suggestion for improving the clamping system...
7. Do the sums on a gantry that is to deflect less than the 0.01mm you have set which has also to accomodate the other inaccuracies in your machine that in the z direction. It may be that you don't require to control 'Z' to the same accuracy as 'X'&'Y'
Ans: The precision in all axes i wanted from the machine should be not greater than 0.01mm .. I am thinking of no-flex, 0-alignment Gantry and Z-axis...
8. Do some preliminary design work. The motors need to drive your gantry and the mass to be moved and the speed required will indicate the sizing of the motor. You have two additional considerations - How do you drive the gantry (one sided drive has issues with judder due to the axis twisting and most special builds use separate but linked ballscrew drives on each side of the gantry)? - Is the stepper resolution and linearity suitable for the application? Steppers have their own rotation inaccuraqcies in athe way a single revolution is divided as all the steps have a possitional tolerance. The use of linear glass scales with the scale used as the feed back element with servo motors not steppers is the way most designers go.
Ans: I am currently brain-storming and need suggestions from you before putting the design in computer... I am keeping in mind the heavy cutting forces, acceleration deceleration, inertia of the system, precision, rigidity, heavy weight etc...
I will drive the X-axis with two motors along the two sides not with one motor in the center... This will reduce the racking issues.... I will again look into the servo system and glass scales ...
Kind regards and hope the budget is big enough ( No..I have limited budget.. But the Plus point is that I have all the material (Structure steel, machines, manpower) except servos, linear slides and ball screws available with me)Pat
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