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slowing my drill press
Bruce wrote:
I use my drill press mostly to drill metal...very little wood, yet my press, which I was given, was intended to drill wood, so it really runs too fast. I have it set at its slowest ratio setting, but still I think it is too fast. I am planning on switching out the belt pulleys to achieve the speeds I should be running for metal. Thus the questions.....what is a good speed range to target for and what is the formula for pully size? I would like to stay with a set of three step pulleys and have a nice range of metal speed cutting. Most of my drilling is 1/2 inch thickness or less. Too slow is better than too fast....I would guess...right?? Thanks I don't recall having seen a drill press that went too slow. Most all of them are damn scary at upper speeds. One of mine is an older Rockwell and I tried the fastest of the 4 speeds but didn't cut anything. I don't ever use the next fastest speed either. I've had that press since 1978 IIRC. michael |
slowing my drill press
On Thu, 17 Jul 2003 08:31:24 -0700, michael
wrote: Bruce wrote: I use my drill press mostly to drill metal...very little wood, yet my press, which I was given, was intended to drill wood, so it really runs too fast. I have it set at its slowest ratio setting, but still I think it is too fast. I am planning on switching out the belt pulleys to achieve the speeds I should be running for metal. Thus the questions.....what is a good speed range to target for and what is the formula for pully size? I would like to stay with a set of three step pulleys and have a nice range of metal speed cutting. Most of my drilling is 1/2 inch thickness or less. Too slow is better than too fast....I would guess...right?? Thanks I don't recall having seen a drill press that went too slow. Most all of them are damn scary at upper speeds. One of mine is an older Rockwell and I tried the fastest of the 4 speeds but didn't cut anything. I don't ever use the next fastest speed either. I've had that press since 1978 IIRC. michael Put the "motor" pulley on a jackshaft and put another set of pulleys between the motor and the other end of the jackshaft. If you duplicate the current setup, and have a 5:1 ratio now, you can get 25:1. |
slowing my drill press
I'd say 100 sfm is close to a maximum. if you scan machinery's handbook,
you'll see numbers from 60-100 for HSS in steel. using a factor of 4 instead of 3.14 grosses up the speed by almost 30%. You also forget to convert the dia into feet. @ 100 sfm ..5" = 760 rpm, .125" = 3000 @ 60 sfm ..5" = 450 rpm, .125" = 1800 there's always lots of reasons why the practical speed is less than the theoretical. I find this especially true on drill presses which are less rigid than most of our other machines and (comparatively) often take larger cuts. I agree, there is nothing wrong with running slower, theoretical maximums guide commercial ops where time=money. as a reference, on my 18 buffalo, speeds (with at 1725 rpm motor) are 400,700,1100,1750 & 2800. For anything over 1/2 inch, I'm more comfortable using the mill. cheers "Gary Coffman" wrote in message ... On 17 Jul 2003 06:17:56 -0700, (Bruce) wrote: I use my drill press mostly to drill metal...very little wood, yet my press, which I was given, was intended to drill wood, so it really runs too fast. I have it set at its slowest ratio setting, but still I think it is too fast. I am planning on switching out the belt pulleys to achieve the speeds I should be running for metal. Thus the questions.....what is a good speed range to target for and what is the formula for pully size? I would like to stay with a set of three step pulleys and have a nice range of metal speed cutting. Most of my drilling is 1/2 inch thickness or less. Too slow is better than too fast....I would guess...right?? RPM = SFM/(4 * dia) Where diameter is in inches and SFM (surface feet a minute) for mild steel is about 100 (different materials have different SFM requirements). So the smaller the drill diameter, the faster it should turn. For example, a half inch bit should turn about 50 RPM, but an 1/8 inch bit should turn about 200 RPM, a 1/16 bit should turn about 400 RPM. Etc. Aluminum would be about 8 times faster, cast iron about 20% slower, etc, because they have different SFM cutting speed requirements. In other words, cutting speed is determined by the diameter of the hole, not the depth. If you drill more than about 4 diameters depth, it is called deep hole drilling, and you may have to "peck" drill to deal with chip extraction. The speed reduction formula for pulleys is simply the driven pulley diameter divided by the driving pulley diameter. So a 6 inch pulley driven by a 2 inch pulley would have a 3:1 reduction ratio. Thus if the motor turns 1750 RPM, the spindle will turn at 583 RPM. Gary |
slowing my drill press
ok, didn't pick up on 4 being both pi and inches - feet, but I think
there's still something missing cuz the speeds you came up with are way to low (imo)- ie 50 rpm for 1/2" drill. Moltrecht gives the formula for cutting speed as rpm=12*fpm/pi*D". if you factor out pi, you are left with rpm=4*fpm/D", not fpm/4*D which for the 1/2" hole = 800 rpm. Personally i find cutting a 1/2 hole at 800 rpm a little hairy and would run my drill press at its slowest speed 400, giving a fpm rate of about 50. Michael "Gary Coffman" wrote in message ... On Thu, 17 Jul 2003 12:20:48 -0700, "Michael" wrote: I'd say 100 sfm is close to a maximum. if you scan machinery's handbook, you'll see numbers from 60-100 for HSS in steel. using a factor of 4 instead of 3.14 grosses up the speed by almost 30%. You also forget to convert the dia into feet. No I didn't. The "factor of 4" as you call it is actually 1/4 which is close to 3.14/12. So both the diameter to circumference conversion and the inches to feet conversion is taken care of in that one number. It is a standard machinist formula you'll find in most of the texts, Moltrecht for example. Gary |
slowing my drill press
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slowing my drill press
You have a choice between.a VFD drive or adding a jackshaft to the
existing drillpress. I had this problem, but had difficulties in getting another pulley that matched what I had. I could get the diameters, but the spacing between the steps was wrong. Anyhow, I made a pulley. You can see how I added a jack shaft to my drill press on my website under my Projects Page. There are a number of ways you can add this jackshaft, and its not a hard project to do. Cheaper by far than a VFD drive. I don't think there is such as thing as being too slow, especially with a drill press. Have fun On 17 Jul 2003 06:17:56 -0700, (Bruce) wrote: x-I use my drill press mostly to drill metal...very little wood, yet my x-press, which I was given, was intended to drill wood, so it really x-runs too fast. I have it set at its slowest ratio setting, but still x-I think it is too fast. I am planning on switching out the belt x-pulleys to achieve the speeds I should be running for metal. Thus x-the questions.....what is a good speed range to target for and what is x-the formula for pully size? I would like to stay with a set of three x-step pulleys and have a nice range of metal speed cutting. Most of my x-drilling is 1/2 inch thickness or less. Too slow is better than too x-fast....I would guess...right?? x- x-Thanks -- Visit my website: http://www.frugalmachinist.com Contents: foundry and general metal working and lots of related projects. Regards Roy aka Chipmaker // Foxeye Opinions are strictly those of my wife....I have had no input whatsoever. Remove capital A from chipmAkr for correct email address |
slowing my drill press
Bruce wrote: I use my drill press mostly to drill metal...very little wood, yet my press, which I was given, was intended to drill wood, so it really runs too fast. I have it set at its slowest ratio setting, but still I think it is too fast. I am planning on switching out the belt pulleys to achieve the speeds I should be running for metal. Thus the questions.....what is a good speed range to target for and what is the formula for pully size? I would like to stay with a set of three step pulleys and have a nice range of metal speed cutting. Most of my drilling is 1/2 inch thickness or less. Too slow is better than too fast....I would guess...right?? That is exactly correct. Going very slow will naturally increase your machining time but unless you a drilling a lot of holes you will typically spend much more time in handling then cutting. If you go too fast then you have to make sure you are feeding quick enough to produce a chip. As soon as you fail to feed quick enough to produce a chip the drill bit will begin to abrade instead of cut and your cutting tool life will be drastically reduced. Besides this you have to contend with keeping the drill bit from overheating. The only real downside of going too slow for someone not on the clock is that your surface finishes will typically suffer from the higher feed rates. This is usually offset by the fact that your cutting tools will be sharper and potentially last a long time. One word of caution- low speeds usually mean high torque and when you are using a drill press you frequently hold the parts by hand, so be careful, especially when the drill breaks through and wants to thread up on the helix of the bit. If you frequently drill thin parts I would highly recommend the varibit drills. Thanks |
slowing my drill press
In article CyIRa.85723$H17.27201@sccrnsc02, "Bob says...
Probably an 1100 rpm motor would be hard to come by in an AC machine. That'd be a 6 pole machine, synchronously speaking. Pricey? Actually it was not much more expensive than the 1725 standard motor. I almost went that route when updating the drill press at work, but I do a fair amount of small stuff, and the slower speeds on the VFD still give plenty of torque. I think the slower motor was maybe 20% more money. Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
slowing my drill press
"Bob Swinney" wrote in message news:CyIRa.85723$
If real slow speeds are wanted, then a 1100 rpm motor can be used. Probably an 1100 rpm motor would be hard to come by in an AC machine. That'd be a 6 pole machine, synchronously speaking. Pricey? Bob Swinney Depends on where you shop. I have picked up several at the scrap yard for the same price per lb as any other motor. New they are also about the same price per lb. They do weigh more for the same horsepower, but weigh about the same for the same amount of torque. Dan |
slowing my drill press
I want to pass along a tip my wife's 80 year old uncle showed me in his
work shop. It was simply an old wash machine motor mounted vertically on drill press so that pulley on motor lined up with 4 speed pulley on drill press motor. The regular motor is not turned on but is turned by aux. motor. giving quite a speed reduction. I am now rigging one up on my drill press to slow down drill for over 3/8 " drilling. Aux. motor will be fasten to 1 1/4 pipe that will slide over smaller pipe with a pin to hold it at right height for pulley size I want to use. A spring will keep tension on belt. For regular drilling of smaller holes the regular motor will be turned on to use. I think the aux. motor just runs idle. If not I will just unbelt it. This is what I posted in 1998 and since then have used it several times with good success. Dale |
slowing my drill press
In article , Dale says...
I want to pass along a tip my wife's 80 year old uncle showed me in his work shop. It was simply an old wash machine motor mounted vertically on drill press so that pulley on motor lined up with 4 speed pulley on drill press motor. The regular motor is not turned on but is turned by aux. motor. giving quite a speed reduction. If I get this, it sounds like the regular motor is being used as a jackshaft for speed reduction. Cute idea! Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
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