Cutting Thin Slots

dylan said:
Hi,

I'm really new to this type of thing, I don't even have any of the machines. I make furniture and want to make some of my own hardware. I also make hand saws.

I was wondering what the best machine and setup would be to cut a thin slot, .020", about 1/4" to 3/8" deep, into brass bar, maybe 10"-14" in length.

I was thinking a slot saw blade or a micro drill bit. Would a horizontal mill or vertical mill be better? From what I have gathered it seems like a vertical mill is more versatile. Can anyone recommend a good entry level machine?

Thanks for any advice.
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I agree with the vertical mill and slitting saw for that deep of a cut. The cutting length on normal end mills is 3 times the diameter, and the shank will likely be 0.125 diameter so you cannot cut deep enough (you need 13 to 20 times the diameter). For a slot this narrow and deep , you would have a real tough time clearing the chips with an end mill, and the side force would likely break the end mill anyway even if you could find one long enough. Furthermore, the depth of cut on each pass should be about 5-10% of the diameter for small end mills (.001 to .002 in this case) requiring several hundred passes to make the cut.

As for horizontal vs vertical mills, I would get a vertical mill and perhaps an angle head that allows using the cutter like in a horizontal mill. I have this set-up and it has served me well when I needed to do a horizontal milling operation. The right angle heads can be a bit pricey ($maybe $500) on E-bay, but they use the same R-8 collets and fit the column allowing easy vertical adjustment if needed.

Be sure to purchase large enough diameter slitting saws to allow for the arbor, which uses up a significant fraction of the diameter. I have an arbor that fits several different ID saws, but it has about a 1 1/4 inch diameter, so a 3 inch slitting saw is limited to a little under 7/8 inch depth of cut.

bridgeport right angle head.jpg bridgeport right angle head.jpg
 
You could also make the cut in a lathe if the slot goes out the ends of the bar (a blind slot would be tuff). You would have to start with a piece longer than what you need and cut it off later. With the piece mounted as if to turn it, lock the spindle and use the carriage feed to cut the slot. You would need a relief cut, ground or drilled into each end of the slot and grind a HSS lathe bit as a form cutter. (Like a .020" cutoff tool rotated 90 degrees) You run the carriage like it was a shaper. To get the jist of this you could watch a multitude of utube vids in which they cut gears on the lathe in much the same fashion. As you can imagine, light cuts and patience will be the order of the day.
 
Thanks for all the suggestions and advice.

I'm trying to decide whether or not to get this small grizzly horizontal mill or go for a vertical mill or a lathe with a vertical milling head attachment. The later two seem to be much more versatile, and the lathe would allow me to make my own brass screws and nuts and bolts and other hardware which I would like to do in the future. My only concern is whether the lathe/vertical mill set up can cut the slot as consistently as the horizontal mill, it is essential that the slot be parallel and uniform so that the saw blade is kept straight.

Here is a picture of what I am trying to accomplish, sorry the resolution is so low:

http://www.blackburntools.com/new-t...lotted-backs/images/list-slotted-backs-03.jpg

It seems like you guys are saying the vertical mill with the appropriate fixture would be able to accomplish this, so I'm thinking that is the move to make. Any thoughts on this particular machine:

http://newlondon.craigslist.org/tls/5204522000.html

or this one:

http://hartford.craigslist.org/tls/5151687932.html

or this:

http://newhaven.craigslist.org/tls/5211995823.html

Am I way off base with these machines?

Thanks for all the replies so far, I really appreciate the help and advice,

Dylan
 
I like the third mill machine. I prefer using s slitting saw with the proper diameter arbor since your slots look thin and shallow in the photo.
 
I would definitely avoid the first CL listing, what you're calling a lathe/vertical mill and the rest of us call a 3-in-1 machine. The cross slide travel on these is rather limited for what you want to do.

The other two will work but the last one is a more common and useful configuration.

It sounds like your work is going to be on the small and light side and I'm wondering if a mini-lathe and mini-mill might not be better suited to your needs. A mini-mill will definitely cut brass stock accurately enough for your needs and unless you plan to do a lot of general milling work it may suffice.

The same goes for the lathe. The attitude in most hobby machining circles is to go as big and heavy as you can afford to go but I can tell you that for smaller precision work, a small precision lathe is a better choice. If making small hardware, screws and bolts is in your future you will find it more difficult to do on a bigger lathe. And smaller machines will be cheaper to buy new.

This is a very slippery slope you're on and the best guideline I can give is to be very clear on the scope of work you need these machines to do, then decide.
 
I'm not familiar with the Grizzly mills, Dylan, but I like that the G0781 has a square column, variable speed and and an R8 spindle. I'm not sure it will slot your brass piece in one go but a fixture can be made to enable it.

Why not search the forum for threads on purchasing a new lathe to see if that gives you the info you need. If not, then start a new thread and state your intended use and needs. There are lots of guys with Grizzly machines here and they may be able to give you specifics.

I had a look at your site (nice stuff, by the way) and given the stuff you are selling there I think you could get by with Sherline tools. I raise this option because of the size of your work. Sherline lathes and mills are very small but they are also very capable machines. The start up costs and costs for accessories would be more manageable, too. Something to think about.
 
Thanks Mike,

I'll search around the forum to see if I can find any reviews.

I'll look into the Sherline option, thanks for the suggestions. FYI, that isn't actually my site, I just found that picture as an example, hopefully one day I'll be able to produce similar quality items, that's the goal.

Dylan
 
Dylan ,

Could you not get folded over brass strips to make the back saws ........ that's how it used to be done. When you put the blade in it you used a hide hammer to complete the folding by hammering it on a soft lead slug so you didn't bruise the brass or distort the line of the blade.
You can also use a press to fix the fold to the blade .

If you use a lathe to mill or slot , cut a few inches at a time & it wouldn't be long before you'd got the whole length done . Though you'd have to turn it round once you gone past the half way point so you have some thing to grip on at the tool post . Again you'd have to press the brass back on to the blade or use an industrial grade metal glue
The type of tool post clamp wold be very important ..the modern quick change tool post tool holders could work if they have a wide enough mouth for the brass to fit in . failing that making a square bridge to go over the brass as a good fit over a length of say 2.5 inches and using an over the center clamping arm would also work if you can get it tight enough .

If you have a small drill press vice you might also try and see if the vice can be mounted on the cross slide and see if you can do it that way with the slitting saw blade on an arbor in the lathe chuck ( maybe even on a long arbor /shaft between centres ) .

Brass gets a bit squeaky & tight when you cut /turn it , possibly due to it getting hot and expanding , so be prepared to only do a small cut and let it cool for 20 minutes or so lest the blade grabs in the slot you've cut and breaks.
 
Hey David,

Yeah I could get the folded back, I also found a guy who sells the slotted backs too. I have this weird complex about doing everything myself though, I mean if I had the time to mine the ore myself I probably would be on that forum too.

I tried to build a metal break with plate steel and heavy duty door hinges to bend the backs myself but I could get the brass to work with me, and it was 260 brass which I read was the most malleable. So at that point I considered buying an industrial break, but figured if I was going to make a serious investment the lathe would be more versatile, plus I like the slotted look.

As it is now I am laminating two brass pieces to the saw with JB Weld and pins. It works pretty well to be honest, just takes a long time and makes a mess.

My plan now is to get a vertical mill and a vise that can hold a fixture that itself holds the brass back and use the table movement to progress the vise/fixture/brass.

What would you recommend for lubricant/cutting fluid? Anything different when cutting brass?

Dylan
 
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