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| Deep hole drilling 101 on lathe? |
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| shaddr3:
You are using a gun drill in the tailstock or a different type of bit? I was told gun drills needs to be fed at a consistent rate and NEVER reversed while spindle is in motion. I'm building a machine that makes snow in the winter when temperatures allow, trying to build an all in one unit design. I plan on using a gun drill that will fit in a boring bar holder. Modifying my lead screw as my lowest feed rate is .004", and i'm aiming for .0005" (Which is the norm for gun drilling). Spinning at 2000rpm, it should cut 1"IPM. You're right David. A machinist that used to work for Beretta many years ago told me it's best to rotate your bit in the opposite direction of the spindle as this will help keep the bit straight and also increase your desired SFM. In my case my material is aluminum, which my sfm is much higher while trying to avoid chip welding on my bit. Right now i'm focusing on the best method for the lead screw. |
| PekkaNF:
I'm not planning to use the standard tail stock for any deep hole drilling, everything wrong with it. I am planning to try out trough cooled twist drill first. Less pressure requirement and more relaxed feed requirements. My primary lathe is not good for anything more demanding. It's only about 150 kg 500w single phase motor. If that does not work plan b is to start toying with piece of crap capstan lathe I have. It has no tail stock, chuck is crap and lead screw is missing. It weights close to 1000 kg and has a gearbox plus about 4 hp 3 phase motor. Spindle speed goes up to 2400 rpm. I.E. it is perfect base for lathe/vertical drilling machine. But plenty of work for few holes.... You probably have found this thread: http://www.practicalmachinist.com/vb/general/gun-drilling-lathe-192962/ Some parameters: http://www.sterlinggundrills.com/printer-friendly/gundrilling-guidelines.pdf http://www.sterlinggundrills.com/speed_and_feed_charts.shtml interesting picture here: http://www.practicalmachinist.com/vb/general/shop-made-tool-pics-201261/index5.html#post1400560 Pekka |
| PekkaNF:
Not sure if this ever going to be much use of anybody or I get anywhere, but I lets see. I bought three long spiral drills stubby ones are 8,5 and 9 mm diameter and just over 100 mm long. The long one is 10 mm diameter and business lenght is 185 mm. Local toolshop was selling them out, these were smallest ones they had. Exact drill types are (if anybody is interested): STOCK 71553 DIN 341 V70-IK Ø8,5 x 250/100 mm STOCK 71553 DIN 341 V70-IK Ø9,0 x 257/107 mm STOCK 71567 DIN 1870 V63-IK Ø10,0 x 335/185 mm All are MT2 taper shank with side coolant feed. They are trough cooled. Just close enough to work with tempered steel, but not much room for error. The side coolant feed is cylindrical ground surface, very close to 24 mm OD and 30 mm length. Should not be very hard to make coolant mount (inducer?) to it. Bit more lost with coolant pump requirements. I see sealed collets advertized for cylindrical shank and up to 1000 psi (about 60 bars) that probably gives some indication of max required pressure. I wonder if those drill operated transfer pumps could be used to test or do I need to source a car motor oil pump or small gear pump (hydraulic pump) for it. There is some more work to do, so don't expect any results tomorrow (or next week:). On this picture I'm gloating my spending on local tool shop. They had some guide dog calibers for sale and they said that they really don't suck really that much. I like that kind of sales talk. Pekka |
| PekkaNF:
I have been googling and calculating stuff, it all starts to look achievable. Not too easy, but not outright impossible either. I have to work on three fronts: 1) Coolant inducer. This I think is easy one. Lot like that: http://www.carbideanddiamondtooling.com/thumbnail.asp?file=assets/images/yg1usa/spadedrills/spade_drill_rci.jpg&maxx=750&maxy=0 2) MT2 taper holder. I do have a MT2 taper holder for the cross slide. I am not 100% sure it will be able to hold drilling forces and bit unclear how to put drill bit absolutely straight without test bar. Maybe between spotted pilot hole on the bar under drilling and MT2 holder end on tail stock? * I can gear down correct machine feed on cross slide no problem. * Probably really should build a separate tool holder for drills. Plan B: to build a separate tail stock from scratch to allow 300 mm of feed. I have a TR16*4 mm acme rod + nut + geared 24 VDC servomotor, but no electronics. maybe something like this: http://www.practicalmachinist.com/vb/attachments/f26/77378d1369344103-schaublin-capstan-handle-tailstock-20130302_110946.jpg Or like in capstan lathe - like capstan lathe ram. It all looks pretty doable. some serious work thoug. Something like this: http://static.wixstatic.com/media/999e2a_e754617990544f3acc20dda4e9e08855.jpg_srz_620_360_85_22_0.50_1.20_0.00_jpg_srz 3) High pressure coolant pump. I probably need 20-40 bar pressure and low flow. Just have figure out what kind of madmodder pump I am looking for? Oil transfer pump? Car engine oil pump, small hydraulic pump? Ideas? Pekka |
| shaddr3:
Pekka, I really want to see you accomplish your goal, and like yourself i've spent hours on end over the past two months figuring the best method as well. Local machine shops want to charge as much just for ONE drilling than the entire costs of parts and materials of TWO finished units. I came across a post on practical machinist months back where someone had built an adapter that connects their carriage to their tail-stock, which may work if you can adjust your lead screw to your needs. Attached is a picture and documentation of Sterling's suggestion for mounting the gun drill bit to the cross slide. I'm also skeptical about using a tool holder on such a long bore, but their adapter suggestion is much more rigid. If you already have the servomotor and want to utilize it further down the road, they sell off the shelf controllers for nearly pennies to adjust the speeds via a dial/potentiometer. I've just been worried about setting mine (stepper motor) up on my lead screw and not being powerful enough for my feed rate, slowing it down. Stalling can also damage the motor. So i've been having trouble calculating the best torque motor for the task. I myself have been trying to determine the best pump to use. A high pressure coolant pump would require a complete enclosure around your material, with a reservoir & filtering system. I have several high pressure pumps but unfortunately are 2.5gpm-13gpm. I did build a pump setup years ago with a Hypro dual piston pump, which I think go as low as 1.5gpm and 34bar, still too high of a flow rate. It had a hollow shaft so I direct connected to a 3/4hp electric motor. I'm sure you've already seen the post on practical about a member using an automotive power steering pump instead of buying Sterling's Spraymist system. Though i'm pretty sure average PS Pumps are 2.5gpm+. Check out http://unist.com/ they have a product very similar to Sterling's but a couple hundred dollars cheaper. They also offered me a 30 day trial. Still $900 for a system :bang: not quit in my budget. Unist's system along with their lubricants (which are 100% green) can be operated without any extra coolant exiting the bore so no mess. I really like those drills you picked up, any ideas on US suppliers that sell them? I hope this helps, as i'm new to this as well. I'm still waiting on unc1esteve's response. |
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