| | |
curious to know for these low horsepower benchtops do you use aluminum which is twice as expensive or mild steel ?
Aluminum is about three times the cost of cold rolled steel, but only about one third as dense, so a given size bar is about the same cost in either material. One major problem with aluminum many people don't know is that it's modulus if rigiidity is 2.5 times lower than steel. So for any given section and load, the deflection would be 2.5 times great. Harmonics could be even worse than this factor because of less mass to dampen.
but you did not say what steel do you mostly cut on your benchtop mill
I'm not doing any CNC milling yet (although I am gathering parts to convert my SX3). I'm new to milling in general, but I've only been milling 4130 so far. The metal that I use for a given project is going to depend on what it is I'm making.
I'm sorry, I thought you meant you were considering whether to build a mill with an aluminum structure vs. steel. I don't have a mini mill, I have a 42" x 20" x 24" vertical cnc with box ways, 20 hp and 8,000 rpm. The same principles hold true. Minimize the tool length and holder length. Get the cutting edge as close to the spindle bearing as you can. Higher helix is better (45 degrees) even for mild steel. If a four flute face mill chatters, try three edges instead. Variable helix endmills rock. I would try a 1/4" variable helix endmill. No endmill holders. That just adds length away from the bearing. I would collets and choke up on the endmills. I did that when I was running a Bridgeport and had much better results.
Dave
good info; I think I'm going to check out your other posts- but, I want to know; is it more economical to work aluminum or mild steel; given the softness of alum, it's cost versus cost of increased the tool wear cutting mild steel, and long term wear on the mill ? would you care to render an opinion on that sir ?Originally Posted by davereagan
Aluminum, whether 6061, 2024 or 7075, will cut like butter compared to steel. If you must use mild steel for strength or rigidity, try to get 12L14, which is leaded for free cutting but actually has a little more strength than standard mild steel (1018) 12L14 is only available in rounds, squares and hex shapes. Flat bars, I use 1018. The difference in tool wear on steel vs AL is as wide as the difference in cutting speeds and forces. With a solid carbide endmill, you can cut aluminum for months unless it has silicon, which is very abrasive. For aluminum, generally there is no speed limit for milling, just what your spindle can do. Lubrication is important because it has a low melting temperature and will gall easily if run dry. For an open mill with no flood system, Tap Magic works well and a 4 oz. can goes a long way. High helix endmills made for cutting aluminum really make a difference. I've used them even for mild steel in light cuts to reduce chatter and get a cleaner finish. Try www.kbctools.com They have stores in Canada. The top of page 148 has some very reasonably priced endmills for aluminum. They work well. Made either in Poland or Korea. They will cut so much more freely than a standard 30 degree helix general purpose endmill, you'll never go back. For 1/4" slotting, I bet you could go full rpm, .125" deep and .002" feed per tooth. If you have 3000 rpm, that's 12 ipm. Possibly more feed or depth of cut. Feel free to email me with more questions: davereagan@hotmail.com
Fantastic information. I will. Thank you.
Laszlozoltan:
Give us an idea of what you want to make, someone can then make a suggestion of what material to suggest that you use. A TON of things are made from billet Aluminum, probally 95% + of what we machine is Aluminum at work.
I have nothing specific right now; I just ordered my mill on friday- I'm going to do some wax models- check them to see my tolerances then move on to metal parts- most of which can be done in alum which a supllier informed me will cost about twice that of mild steel, but I have to offset that cost with tool wear and wear on the mill as well. davereagan basically settled the issue for me with his post above.
Is there any dealers that sell remnants in your area??. Where I live there are several and Aluminum can be had for $ 1.50 per pound. The local metal metal supply has huge stocks of remnants in brass, steel, copper,iron,etc. Another source would be the machine shops as they often have tons of small pcs that they cant use & sell to the scrap guy for pennies per pound. I have bought a bunch of Aluminum this way and often shop around. ebay even has sellers from Canada that sell remnants.
One place wanted $140.00 for a 12ft length of 5\8 hex stock and down the street I purchased the same for $ 60.00. With the higher costs of materials from just a few years ago shopping around can save you $$$.
What about copper?
I have project which would be better served if it were copper, but 6160 aluminum is a fallback. There is thermal transfer involved.
Posting Permissions
| | |
LinkBack URL
About LinkBacks
