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Drilling holes with a PM935, and...

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kb58

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The PM935 mill comes with an R8 spindle. For several reasons I decided to go with ER32 collets, so for drilling holes, there's the choice of getting a chuck with a straight shank that mounts via a collet into the ER32 holder, or remove it and use a chuck that mounts directly into the R8 spindle. Which way do you recommend and why? I'm asking because I want to make sure I'm not overlooking an obvious reason for why it should be one and not the other. I imagine the answer will be "it depends", but I'd still like to know. The one reason I can imagine going with R8 is that it removes the play and inaccuracy in the ER32 setup, but at 0.0002 runout, that much error for drilling seems small. What say you?
 

ttabbal

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Remember that drilling is not a precision operation. The runout with decent quality parts is not an issue for drilling. If you want a precise hole, you need to bore it. Though reamers might be close enough depending on the requirements.

Straight shank is nice because you don't have to remove the collet adapter. It's the same as swapping end mills. Down side is that it takes up Z. You have Z to work with, but it's something that you should be aware of. Either way there is a few inches of knee movement required when swapping between drilling and milling. Some form of power feed is really nice there.
 

Bob Korves

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The chuck will not very likely drill holes to the same accuracy as the R8 spindle has. Proper spindle runout should be within a couple tenths, and high quality chucks can be within a couple thou and still be within specs. Adding a drill bit to the equation usually makes for less accuracy yet. That is OK, drilling is not a precision operation. As stated above, if you need an accurate hole, it will need to be bored and/or reamed to final size and location.

With that out of the way, I prefer straight shanks on my drill chucks for use in everything except the lathe where they are Morse Taper. The straight shanks can be cut short (1 to 1 1/4" shank), will still hold tightly, and will be much faster to change out for other tooling, whether in R8 or ER collets. They will also clear the setup with less or no vertical quill or table movements. That can save lots of time when there are multiple operations on each hole. You really will get tired of changing out R8 or ER tooling for each hole in a sequence of holes, from drill, to countersink, to tap, etc. Try your best to not have to touch the R8 drawbar or the ER collet nut for the entire job. It will be a lot less effort.
 

mikey

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Not much to add beyond what Bob and ttabbal said. Just wanted to help you visualize how your tooling changes will work. Anytime you have to change out an R8 collet you have to loosen the drawbar, tap the top of the drawbar to break the collet loose, completely unscrew the drawbar and then drop out the R8 collet. Then you put the next R8 thing in the spindle, insert the thing that goes into the collet and then tighten the drawbar. This is why a power drawbar has so much appeal; it makes this process so much faster. As noted, removing tools and collets require a lot more room in Z, which may mean you have to crank down the knee before removing the tool/collet, then crank it back up to resume work.

Tools will usually have either an integral R8 shank or a straight shank. If it has a short straight shank then you can just loosen the drawbar, drop out whatever tool in in there and insert the next tool if it fits the collet that is in the spindle. Say you decide to put a straight 1/2" shank on your fly cutter and drill chuck. With a 1/2 R8 collet in the spindle, switching from the fly cutter to the drill chuck simply requires you to loosen the drawbar, tap it to loosen the tool, the tighten to install the new tool. Very fast and takes very little room in Z. This is what Bob and Travis were saying.

The reason I like and use the Tormach TTS system is because most of the tools I use on the mill have TTS adapters that mount the tool into a 3/4" R8 collet. I can go from a fly cutter to a drill chuck to an ER-32 chuck in seconds, without having to move the head/knee because the shank of the tool holder is only about an inch or so long. Loosen the drawbar, tap, change tools, tighten the drawbar. It takes all of 10-15 seconds to change tools. There are faster, more accurate systems to be sure but not at the price of the TTS system.
 

petertha

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I'm confused. If you have an R8 spindle then your current setup is R8 shank > ER collet > cutting tool. Lets call that 2 potential runout sources if we eliminate the drill for now. If you replace this with a dedicated drill chuck it goes R8 > chuck > cutting tool, so 2 sources. If you buy an integral shank drill chuck and/or spend money on precision jaw, you will minimize this & be as good or better than ER in my opinion. If you go R8 > ER > drill shank > drill chuck, you have introduced 1 or 2 added runout sources.

Aside from some debatable convenience I don't see what it accomplishes. For one thing it probably would only be for small drills because you are stacking tooling together. Even a 3/8" chuck is quite long, thi sis gobbling up headroom. Another thing is ER system only achieves stated accuracy with stated minimum torque. This has been documented elsewhere but it translates into surprising gronk in the bigger sizes. Another issue is the big ER nut will likely not play nice with small drills & likely small parts, you may find it 'in the way' more often than you realize, but this is purely a function of project. Just some random thoughts, I am no pro.
 

RJSakowski

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For drilling, I had migrated towards holding the drills in R8 collets. It minimized runout and decreased the overall mounted tool length. On the round column mill/drill, this was important as it provided the overall length of the drill closer to that of the other tooling, eliminating the need for moving the head up for clearance. However, I also had a number of drill chucks mounted in R8 adapters as well as some smaller chucks with straight shanks that I mounted in R8 collets.

When I bought my Tormach mill, I also bought the TTS tooling system. I also use it on my mill/drill because it provides quick tool changes with repeatable tool offsets. The TTS package came with six chucks with adapters to the 3/4" TTS shank. Because I can preset my tool offsets, I tend to use them for drilling rather than direct mounting in an R8 collet. There are times when I will still use the R8 collets, namely large diameter holes.
 

Bob Korves

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you have introduced 1 or 2 added runout sources.
If you carefully test and then mark your tooling for where the runout is, and also the magnitude if desired, you can use that information to REDUCE runout with multiple mounts. You have a mill spindle with .0002" runout, a collet with .0005" runout, an drill chuck with .0003 runout. MARK THE LOCATION AND AMOUNT OF RUNOUT ON THE TOOLING WHEN YOU CHECK IT after purchase, making sure to account for all other sources of runout. Depending on how they are clocked when mounted, you will get different results. You could end up with up to .001" or with zero runout, or anything in between with the examples given above. Note that your result can be more accurate than any of the individual components used separately. It takes time to do this, but it is amazingly worth it when you want ultimate accuracy with not so accurate tooling, and most of the measuring is just done one time. If it is not a fussy job, you just slap it together randomly and know you will not exceed .001" runout. You are working from knowledge, not just guessing.
 
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