i dont need donations for dev really. ill wind up with a set of patterns for the larger machine first, timeline unknown, but it would be nice to wrap up within a few months.Originally Posted by heilcnc
if one were to "donate" to this cause, it would be in time spent finding suppliers of hardware, spindles, mechanical, casting, electrical, etc.
i know most of this info is scattered through the many thousands of build threads on this forum. the relevant ones need to be consolidated here and i cant go hunting.
also, if someone reading happens to make or sell an item that will work on or with this machine that fits the price bracket, please feel free to post a link. dont make a long winded spamvertisement though, if we have questions, they will be asked. for example, if you sell c5 ball screws that can be custom fit to the machine in a sane price ($sub $400 per axis), please provide specs, prices, and contact info.
one key thing we need is a belt drive 30 taper spindle. ive used the "standard" 2.75" bore spec, and gillman, milwuakee, setco and a host of others make high end spindles to fit with a variety of tapers. but they all cost $2500 and up. we need an inexpensive model in the tormack cartridge price range (which is unfortunately too big).
i screwed up something. i cant have large built in mounts on both sides of the table... you couldnt get the dovetail on!
massaged a few things and now its good to go. the ball screw has to be bolted through the top of the table. this is how my sieg kx1 is done, but i dont really like it. im tyring to find a better mounting method that doesnt involve removing the motor mount (but i think thats what ill likely have to do).
so after some though, the x motor mount is separate, but the ball nut mount is integrated into the saddle. easy to install the screw, then the table, then the bearing mount, then the motor. no holes through the table. this DOES limit the choices in ball screws that will fit, but an industrious persont could mill off the mount and make a new on if their needs dictated. to keep compatibility with many brands and models of screw, the ball nut mounitng holes should probably not be drilled.
Have you thought of making the X axes way guides sized to fit a common table, perhaps a X3 or the like?
There may be some after market tables for those machines which may be hardened and ground. The grinding of the table will be a large expense and some people might want to use their current table or go after market.
got a link to the tables? the x3 uses a very poorly designed way system, so id prefer to use nothing of it. likewise, my table is MUCH larger and heavier, and has integrated features designed for CNC making it incompatible with such things. the only table that woul dbe applicable as a "cheap buy" would be the one from the weiss wmd30lv, but its not hardened our ground either and would need extensive machining to make compatible. so even if it can be bought for a fair price, it probably wont make the machine effectively cost less.
the point of all this is to come up with a dedicated ground up CNC casting kit, not rehash the same old same old.
on another note, i refit the base with box ways for fun. i dont think its viable for this mill, too costly... anyone think otherwise? i dont really know how much advantage they would be either. in some ways they simplify the design, in other ways make it more complex.
so i had an idea for versatility. i cleaned up the base casting, and made the wall thickeness more uniform, and opened the front up to allow a better integrated saddle. theres also now less complex machining on the base than before.
this casting is designed, as you can see to take linear rails, or have a dovetail milled in, or even have ground box ways bolted on from the underside.
the bottom is still webbed, but now a closed "bowl". anyone concerned with mass can fill the base with epoxy granite by simply pouring it in. the base is also exactly 12" x 18", so it will bolt down to any cheap surface plate for added rigidity (it was like that before too).
so, the rail/dovetail length is still 18", and the saddle is ~7", so you get 11" theoretical maximum movement. in practice with way covers and a standard column mount theres 9" on dovetails, and a possible 10" on the rails because they can overhang an inch safely - its only the ball return on the overhang, so no load.
the base got a bit heavier, its now 110lbs. i will be bringing it back down to my sub 100lb rule though.
the column will be modified to accept rails as well as the table. there will have to be 2 completely different sets of saddles for either rails or dovetails, and the head is still universal.
the saddle will xy saddle will be fully integrated will ball nut mount points now in exchange for now separate motor mounts which are far easier and cheaper for the builder to fabricate.
thoughts?
Good work - there is a lot of trade black magic in getting the iron to flow well into the mould and only a foundry expert can advise you so it is good that you are talking to some possible casting shops.
The reference to Kempe's will give you the overview on stress relief of iron castings. You basically have three choices or a combination of the three. These are:-
1. Heat treatment heating to arround 550 and 600 'C held for at least one hour for each inch of section thickness. Then controled cooling to 200 'C. Both the heating rate and the controled cooling not to exceed 100'C per hour.
2. Mechanical tumbeling - small parts ?!?
3. Age weathering - i.e. kick the castings out in the yard for several months.
Then depending on the type of iron used for the casting further annealing and heat treatment to give the best machining and wearing surfaces. BUT I can't emphasise too strongly this depends on the type of iron used!
Good luck in your negtiations.
Pat
Hi
I left out the machining is probably best done as a two step process until the stress relief is proven to be satisfactory. Rough out the machined areas and leave for several days for the casting to settle free from any external clamps etc. (Check for movement to see if the stresses have caused movement.) Then machine the final surfaces. A lot of industrial castings are stored in the open air between operations for months not days befor heat cycling became popular - however going green will I guess revert to open air storage for all but the smallest castings.
Again I recommend you look at Kempe's Engineers Handbook. I bought mine several years ago to replace one I got some twenty years previous. Good bed time reading!
Regards
Pat
I would leave the mounts off both ends of the table. It will be hard to machine the dovetails to get a right angle at the mount. The result will probably be that you can't get the mount to travel up flush to the saddle.
Don't try to save weight and machining by casting the dovetail plus a machining allowance. Where the dovetail cuts under bevel the draft the opposite slope. See picture. Casting the dovetail eats tooling when trying to machine to size. Don't ask me how I know.
Alan
Alan,
"Casting the dovetail eats tooling when trying to machine to size." - I'm not understanding what the issue is here. Can you explain?
Regards,
Ray L.
This is a nice looking design - keep up the great work.
I have not seen this machine in person but I thought I'd share the link:
http://www.littlemachineshop.com/pro...ProductID=3503
but from the picture it looks an awful lot like what you are designing. It states it is designed from the ground up for CNC, but my suspicion would be that it is a modified X3.
Perhaps something could be learned from this new machine that can help with your design.
Keith
with the table, have you considered dropping the T-slots and going with a pattern of pins and threaded holes?
reading through this thread: http://www.cnczone.com/forums/showth...t=88499&page=2 some machining time may be saved by using one of the drill/csk/tread mills, and I know alot of people like dowel pins for fixtures.
FS: Complete Z-Axis Assembly with THK RSR15WM slide, leadscrew, stepper mount. PM for more info.
that machine - the sieg kx3 (smithy 622, novakon nm135) is part of the instigator for this. its a good machine, and hard to beat for the cost. mine take that idea and pushes it to another level. mines got bigger travel, a MUCH stronger column, more sigid head, wider dovetails, stiffer base etc. the hope is that in kit form a diy type person will be able to build it out for not much more money than the kx3. turnkey systems from retailers will be more money - for more machine. as mentioned at thie beginning, this machine sits between the kx3 and tormach markets.
im considering casting without slots, or holes and letting the builder add them as needed. i personally prefer the threaded pattern to t slots, but alot of people like t slots and have tooling to match. i would probably leave the drain pockets on either side though.
i think you misunderstood my screwup. the motor mount does not overlap the dovetail, it ir irrelevant in that regard. the issue was it overhanging the bottom of the saddle - and ultimately not allowing the ball screw to be fastened in a convenient manner. so now one side has the bearing mount, one is open.
im not trying to save weight in the casting, i am trying to have less parts to make, and less setups to machine accurately.
so i made provision for a larger ball screw support bearing (20mm shaft FK style). with a simple adapter plate the smaller (cheaper) one can be used, or orther brands that dont follow the bolt and bore pattern of the THK models.
the column is obviously very different. id like some thoughts on this. the old column bolted to the back of the base and centered on a 3" pilot pin. the design is generally strong if theres enough overlap on the mount, but the pilot is a complicated aspect to machine accurately, and as the column got bigger and heavier, seems perhaps a bit difficult to man handle.
the new design is a hybrid. the column will have 4 base bolts and a milled bottom, as well as the milled mating face and 6 bolts. theres a few possible configurations for use:
- mount column and bas to 24" x 18" granite plate independantly of each other. this allows utilization of the full 11" travel on the base.
- mount the column and base on a granite plate as small as 12"x18" for support, then bolt the column to the back of the base to increase rigidity.
- register the base and column on a granite plate, pin and bolt the column to the base, then remove from plate and use as a single unit - put feet under the column and base for example.
the new column aso has integrated nema 23 AND 34 motor mounts inside the back of the column, reducing parts and reducing overall depth of the machine. access to the motor coupling needs to be improved, theres only a small gap at the front of the coliumn right now.
the new column right now is very heavy, 125lbs. so it needs some trimming on the inside.
Possibly he is referring to the fact that most cast iron has a hardish skin that can be several millimeters deep. When you cast too close to the finished size you are machining within this region; with cast iron sometimes it is better if you can take a heavy initial cut to get down into nicer material. This initial cut is one time when conventional milling may be better because the cutting edges approach the hard skin from underneath.
An open mind is a virtue...so long as all the common sense has not leaked out.
If I can make a suggestion: If the weight limit was causing a problem I'd personally set the weight limit per part somewhere closer to 150#. I say this because if it were me moving it around I'd probably want to use a dolly anyway, the parts would only have to be light enough to get on and off the dolly.
what about making the column bolt on top of the base casting like the Haas does then if
you use a surface plate you could use threaded rod Thur all 3 to clamp them and i think
put set screws in all 4 corners of the base of the column to tram it(using slow curing epoxy
inbetween to so the set screws do not vibrate into the cast iron)
doing the column on the base severely limits versaility. basically makes it a single configuration only. it also to me seems to be worst for alignment, basically resorting to shims under the base, reducing rigidity substantially. unless the stress relief is 100% perfect, and the shop squaring them up is perfect.. the mount will need shims, and shims suck. on the back mount desigh, you can tram in one direction, and hand scrape the other, so you have a far better chance of perfect squareness without fancy equipment.
im using the granite as an optional "true base" in this design. the granite is fat to .0005 or better typically, so it makes an ideal reference for mounting, far better then adding a stack of iron underneath.
as for the weight limit, i might move toward the opposite trend actually, and make it even lighter again. people can add their own mass with epoxy granite fill in both the base and the column. the bigger this is getting the more likely id be NOT to buy want it. id like the travels, but i CANT have the weight.
besides, this is priced by the pound. if you wanted 500lbs of extra bulk, you are paying over $1500 just for the iron, or $3000 total for 1000lbs, and a retail more like $7000.. just for the milled castings! out of the question on this project.
reducing the mass to 250lbs to reduce cost, handling, shipping, then having the builder simply pour in a EG mix would probably both be cheaper and work out to be more rigid.
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