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[machinist] 1" endmill ..... which tool holder to use?
- From: Lawrence London <lfljvenaura@gmail.com>
- To: machinist@lists.ibiblio.org
- Subject: [machinist] 1" endmill ..... which tool holder to use?
- Date: Sat, 15 Feb 2014 00:09:53 -0500
http://www.practicalmachinist.com/vb/general/1-endmill-tool-holder-use-280035/
Thread: 1" endmill ..... which tool holder to use?
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1" endmill ..... which tool holder to use?
My mill uses R8 collets, and it seems that the biggest those get is about 7/8". So for a 1" (or larger) endmill it looks like I need one of those holders with set screws. Does anyone have any recommendations for good quality R8 1" toolholders?
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Why torture the machine and yourself? I don't think an R8 spindle can ever use a 1" end mill without a huge sacrifice in stiffness. Besides, what R8 machine has the HP balls to push a 1" end mill effectively? If you need the width of cut, find a face mill or insert cutter body with built in R8 shank.
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02-11-2014, 11:52 PM #3
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If you really need to, get a reduced shank endmill. And yes, 7/8" is the biggest collet in R8.
I use a 3/4", 1/2" shank endmill in my M head with wee bitty 7BS collets and it works well with light cuts.
But keep in mind the limits of your machine. -
To answer your question, I don't think it matters too much what brand you choose, as long as there is a close fit to your R8 taper. Blue it up and check. Send it back if bad.
Concentricity isn't going to be perfect on these or, likely, the fit to your end mills. So what you'll have is a sort of 1" plus or minus a few thousandths fly cutter, running at speeds low enough that balance isn't a big issue.
As others note, this really is way too large an end mill for most conventional uses. Somewhere on PM there is a recent thread that outlines the cases where you might still want to use a 1" end mill in a Bridgeport type mill. I've found them occasionally useful; and that thread will have my and others' notes.
My guess here is that you've come into some nice large shank end mills cheap and want to put them to work? If buying new, just go reduced shank. In any case, you probably don't want to spend the $$$ on a super duper nice Weldon type holder, given that it will either be rarely used or perform poorly if pushed.
Spend that money on something like a proper positive rake face mill in a size that makes sense for the work at hand. -
Yup, reduced shank is the way to go, you can get a 3/4"shank 1" endmill and then just run a collet, but as has been said, it's going to be hell on a Bridgeport in anything much more challenging than aluminum. Pull your ram as far back as possible to still reach across the work. Run the tabel back as close to the column as possible. Suck the quill in to the stop and lock it firmly. Minimize leverage and you can get away with it, but it's real hard on the puley splines, too. Mill at work won't stay in the high speed dogs in the pulley unless you hold the cap down with your free hand when running a large endmilll or facemill. Has popped out of the dogs so many times, they are rounded and now try to jump out as soon as they are loaded and the quill splines start to rattle.
An advantage to a collet versus a Weldon type holder (with the setscrew in the side) is that the cutter runs truer. To be able to get the endmill in the collet, there has to be some clearance. When you tighten the setscrew, it pulls the endmill to one side, so you are going to see .001 or more runout, depending on wear. You can also pull the endmill further up into the spindle with the collet versus the Weldon holder. -
If you need a 1 inch EM,use one with a 3/4 shank.That way it will fit in a R-8 collet.
Those set-screw EM holder types will add too much length,less rigidness,thus chatter for a 1 inch cutter. -
Lot of good advice here. Wish I'd listened to it before I bought an 1-1/4" indexable end mill.
Since I just did this I'll reinforce two points. One, do make sure your R8 EM holder is in good contact in the taper. My first one was not. Not good, because the second point compounds this problem. And that is that the EM holder adds so much length that you lose PRECIOUS rigidity- which you really will be needing with a 1" EM- and you can really batter your taper with an ill-fitting tool.
I was just leafing through the latest ENCO flyer over coffee this morning and saw what appeared to be integral-shank indexable EM's. That'd be a whole lot better.
If you don't need to be able to create a 90 degree corner with your cut, run don't walk and buy a Glacern 45-deg integral shank facemill. THERE'S a proper cutter for wide cuts with a BP mill. Thank me later.
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Thanks everyone, for all this good info! Yes, I got a deal on some 1" endmills and was itching to put them to work (only cutting aluminum). I have a few smaller Weldons that I've never used because they seemed like a loose fit to the cutters as MikeC and PeteM noted. I always thought it was because they were worn out, but now I understand that's just the way those things are made.
LongTom, I do have a Glacern shell arbor sitting around but no cutters. Those things can get pretty pricey and I thought I had found a cheap solution here. Oh, well.
My plan was to use this for facing cuts, so perhaps the shell arbor + cutter would be good enough (as opposed to springing for one with an integral shank)? -
02-12-2014, 04:24 AM #9
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An R8 collet will not reliably hold a cutter that big in a heavy side cut. If I have to, I use Weldon holders and bring the set screw up almost tight, pull the cutter out against it while rocking the cutter slightly rotationally to be sure I am on the flat, then tighten the screw. I no longer own anything with R8s and good riddance. No matter how tight you get them, they allow the cutter to rock sideways slightly, maybe only millionths, but it is enough to work it down. R8s may be fine for hobby projects where you can take your time on light cuts, but for serious production they are an abomination.
Bill -
02-12-2014, 09:21 AM #11
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02-12-2014, 09:29 AM #12
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02-12-2014, 09:42 AM
Diamond
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02-12-2014, 10:47 AM #14
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Since you have them, you can put them in a spindex on the surface or T & C grinder and cut the shanks down to 7/8". Easy and relatively fast to do. Use 5ST collets for the greater grip length on the flutes, when grinding. Hard turn/grind the shank right down to the top of the flutes.
The 7/8" shank will allow you to push them well up into the R8 nose, eliminating the several inches of overhang that occur with a Weldon holder. Just that lack of deflection and leverage will lessen the pull-out effect from the collet, but it will still exist. However the much shorter path between work and spindle will dramatically increase effectiveness & reduce chatter at appropriate speed.
PS, when griniding the shanks. be sure they don't taper in the least the "wrong" way, IOW, since they are yours for use in your mill, you can back taper them a 1/2 thou or so. Just sayin'. Don't get carried away or they will fret in the collet and the collet fret in the spindle nose. The spindle nose is probably somewhat bellmouthed already anyway if it has wear on it....
smt -
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I had one time found a collet that accepted 1". What a POS! First cut and it pulled out and went flying. If you have to, use the Weldon adaptors and take much lighter cuts.
Josh -
Aluminum.... hmmmm.... trying to wrap a brain cell or two around that with a 1" on a BP.
Originally Posted by borne2fly
Thanks everyone, for all this good info! Yes, I got a deal on some 1" endmills and was itching to put them to work (only cutting aluminum). I have a few smaller Weldons that I've never used because they seemed like a loose fit to the cutters as MikeC and PeteM noted. I always thought it was because they were worn out, but now I understand that's just the way those things are made.
LongTom, I do have a Glacern shell arbor sitting around but no cutters. Those things can get pretty pricey and I thought I had found a cheap solution here. Oh, well.
My plan was to use this for facing cuts, so perhaps the shell arbor + cutter would be good enough (as opposed to springing for one with an integral shank)?
It certainly mitigates a lot of the potential issues everyone has mentioned. If you've already got the 1" EM's, heck, a chinee EM holder is gonna be like $30. It'd be worth that to me just to try it. Keep the cutter speed on the upper end and hit it with WD-40 or A-9 and see what happens. You should be able to get some decent removal- not for production, but enough to justify a $30 holder.
If you push things to the "well, THAT don't work!" point you'll get to see what I call a cutter "stubbing its toe" is like on a BP. The long tool holder flexes then unloads. It's exciting. Bucking bronco of a table. Ride 'em, cowboy! You'll want to tighten down the dogs on the ways some to help mitigate the bucking (if you choose to push things).
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02-12-2014, 03:09 PM #19
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Larger dia endmills on an R8 spindle
I would advise against a one inch end mill adapter. It extends the cutting edges 4 1/2" from the spindle nose. R8 spindles are notoriously limber. They were never intended for heavy milling.
The R8 spindle configuration was employed by Bridgeport before WWII for light milling on small items; the designer never dreaming his creation would become a de-facto world standard and all manner of heavier milling cut forces would be inflicted on its frail structure.
Have you considered shell mills? They have no shanks but instead use a keyed arbor with a pilot and are retained with a big head cap screw. A shell mill thus tucks in close to the spindle nose. A shell mill looks like this:
Lot of 3 HSS Shell Mill Cutters 3 4" Bore Brown Sharpe Weldon Ctd | eBay
An R8 shell mill arbor looks like this:
R8 1 2" Shell Mill Arbor No Name | eBay
When you shop make sure the arbor and cutter match for pilot dimension.
One caveat: shell mill cutters run slower and, because of the larger diameter, require more torque to drive at the same stock removal rate - the old power as a function of torque Vs RPM thing. On larger cutters like 2" and above, its increasingly possible to slip the arbor in the spindle. You can expect the safe depth of cut to diminish in proportion to increase in cutter dia and material strength. My experience on an R8 spindle in a Bridgeport clone suggests about 0.020 DOC for a 4" cutter in steel. The more teeth engaged is also a factor.
Fly-cutters work well for simple facing cuts but they have their limitations. There is only a single cutting edge and feed rates have to be correspondingly slow for a given advance per cutting edge. An 8 tooth cutter may be safe at 8 times the feed rate and there are 8 cutting edges. Other points about fly-cutters is edge wear over a long wide face, safe cutting diameters limitations for the R8 spindle, difficulty with machining shoulders, and actual attainable flatness - the overhang rule applies radially as well as axially - the tool deflects as the square of the overhang and spring-away is some function of the edge wear and tool elasticity. More massive fly-cutter design won't help. The controlling feature is the spindle diameter at the front bearing - 35mm in the case of a typical turret mill - and secondarily the rigidity of the spindle tooling. A 3/4 shank in a collet for example is probably limited to a 4" dia sweep fly-cutter. YMMV considerably.
There is no positive key drive in an R8. There is however a collet indexing pin up inside the R8 spindle. It's intended to index the collet if for some wild reason a collet needs to be indexed to a specific spindle orientation. This indexing pin has no practical value as a driving key. In fact, it will shear off at 100 lb ft or so and the stub will tumble in the arbor keyway scoring the crap out of the spindle bore. Very bad.
My advice is to remove the collet indexing pin forever because it's prone to failure and the damage it causes on failure is astronomically out of proportion to its microscopic value. Unscrew the retaining ring on the nose of the spindle quill and find the hole in the side of the spindle. There are TWO set screws inside: the dog point that's the actual indexing pin and a short one that locks the dog point in place. Remove both. They are an oddball thread so if you ever wish to replace them put them in a coin envelope and put that in a safe place. I suggest you tape it inside the column door.
Oh yeah, replace the ring. No particular torque needs to be set. A good lunge with the strap wrench or face spanner is plenty.
Sorry, long winded.
Getting back to running 1" endmills in R8 spindle. I suggest you look at reduced shank endmills. You can buy cheap sets having 4 to 6 sizes of larger dia endmills in 3/4 shanks with shorter overall length of cut. They work pretty good but you have to be careful of the limitations of import cutters. I've found they run OK but the HSS isn't quite up to snuff.
Look here:
http://www.ebay.com/itm/6-Ps-HSS-End...#ht_2237wt_929Last edited by Forrest Addy; 02-13-2014 at 09:41 AM.
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If the desire is to have an inexpensive and reliable solution for taking wide facing cuts on the mill, use a flycutter. I use brazed carbide lathe tools and have several different size holders with 1/2 and 3/4 shanks. I even have one with an R8 shank. The carbide bit lets me run a faster speed than using HS endmills, shell mills, etc. With a sharp bit with a little radius on the nose, I get wonderful surface finishes.
I have HS shell mills, but would not use them on my R8 mill. (I have 5C arbors for them.) I bought an R8 shank positive rake three insert cutter and only used it once. The flycutters work a lot better.
Larry
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[machinist] 1" endmill ..... which tool holder to use?,
Lawrence London, 02/12/2014
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