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Stephen Hull
Registered
Username: Oliver2257
Post Number: 2
Registered: 01-2007
| | Posted on Thursday, January 11, 2007 - 07:06 pm: | 
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If this is answered in the body of this forum, please excuse this question, I looked first and am not able to estimate it from the plans I downloaded. What is the vertical clearance under the gantry or the tip of the cutting tool per plans built? I hope to place a rotating axis under the gantry to allow engraving on round stock. Thanks |
Gerald_D
Registered
Username: Gerald_d
Post Number: 704
Registered: 11-2005
| | Posted on Thursday, January 11, 2007 - 09:19 pm: |
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Welcome Stephen! This is not an easy one to answer, because the answers will be misleading...
1. Clearance under the gantry is about 200mm [8"] depending on the table top thickness and the height of the main longitudnal channels. This "clearance" does not mean it is practical to put a job in there which is 200mm high.....
2. Clearance under the cutting tip depends on the above as well as: a. the length of cutting tool and b. how high the spindle/router is mounted to the z-slide. This may surprise you, but the typical max clearance under the cutter tip is to the order of only 75 to 100mm [3-4"]. The MechMate's primary function is as a board/sheet processor (MDF, plywood etc), for which the clearances are adequate.
If one wants larger clearances, then the Z-slide needs to be longer. Since the z-slides on all CNC routers are cantilevered or overhung, lengthening them causes a drastic increase in flexing. With the MechMate, it is possible to add more V-rollers to the spider plate so that the z-slide can be retracted higher to give more clearance - without the increase in flex. But this needs a bit more homework. |
Stephen Hull
Registered
Username: Oliver2257
Post Number: 3
Registered: 01-2007
| | Posted on Friday, January 12, 2007 - 05:40 am: |
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Thanks Gerald,Thought provoking answer. Perhaps rather than messing up the geometry of the gantry a modification could be made to the table, keeping the cutting surface of the turned piece in its proper relationship to the gantry. 3 to 4 inches is actually a fairly substantial space and offers flexiility. What comes to me now is a properly sized V in the center of the table where the rotating piece would go, having bolt in center pieces that can be removed for larger turned pieces. Attaching (welding) the V to the now outboard cross members with a reinforcing piece at the apex of the V and some additional reinforce members. That should maintain the table ridgity. One problem, much more steel, more complex assembly. Good thing I have a fork lift. I live near San Francisco, bridges, especially the Bay Bridge with lots and lots of trellis and X bracing. And I am aware that the bridges move. The process unfolds. And I am following your suggestion, gantry first, per plans. This is a great forum! Thanks to everyone for their posts. I have enjoyed hours of the best reading and pictures. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 705
Registered: 11-2005
| | Posted on Friday, January 12, 2007 - 07:15 am: |
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Stephen, and everyone else, the MechMate's Z-slide can travel 200mm [8"]. The z-slide can go from flush_with_bottom_of_gantry down to touching_the_table_top. This is very typical of all gantry routers.
The reality is that nearly everybody mounts their spindle/routers so that the collet is about 50 to 75mm [2-3"] below the z-slide which already knocks that amount off the gantry clearance. Then we want to cut a thick board and so we need a long cutter - long cutters protrude further and reduce the clearance again. Hence the typical discovery that folk cannot cut more than 4" thick on a router with 8" clearance. It is not a shortcoming of the MechMate per se - it is typical across most routers.
If you mount the router/spindle high on the z-slide, at worst the slide hits the wood before the cutter goes in full depth....at best the slide only hits the clamps holding down the wood, or the dust extractor foot, or.....
The easy temptation is to raise the height of the main longitudnal beams so that the gantry is higher off the table. That means the support bearings of the z-slide are pushed further away from the thin sheet cutting jobs. So we get much more flex in the z-slide when cutting the boards/sheets for which the machine was originally designed.
The most practical approach so far is to have higher longitudnals in conjunction with a "removable table extender". This is a box or stage that lies on the table and raises another working surface up nearer to the gantry. Thin stuff is cut on the box - for thick stuff the box is removed. But this brings up all the issues of table stability and flatness...... |
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