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Thread: Drill press speed optimisation
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25th Dec 2016, 09:23 PM #1Philomath in training
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Drill press speed optimisation
Over the last few days I've been trying to analyse the pulleys on my drill press. The graph below shows the issue I have (although not as clearly as I would like). I've done this as drilling speed for steel just to make it straight forward. The dotted line is the current set of speeds and you can see that between about 15mm and 5mm there are no suitable speeds, so a 8mm hole must be drilled at the same speed a 15mm hole is. Unfortunately this is precisely the range where I drill most holes.
Drill options.jpg
The dashed lines are theoretical curves for a logarithmic progression. The grey curve is for a set of pulleys that would give a good distribution for holes smaller than 20mm but loses the slow speeds that come in handy for hole saws and larger drills (don't use them often but I do need to).
The motor pulley has 3 grooves on it but could potentially have 4, so the 12 speed curves represent this. All these options have been done on Excel, trying to hit various spindle speeds while juggling pulley sizes to keep belt lengths the same. As previously stated, the current set up has variations in belt length that puts extra strain on the motor shaft.
The curve 12(1) is not too bad but comes close to doubling up at lower selections. 12(2) has a better distribution but requires a reasonable amount of adjustment (25mm+) for belt tensioning. Neither of them get down in speed to 150rpm that I can currently get (12(2) gets to 190rpm) and I was hoping to get to 120rpm as per the progression curve. A VFD would not necessarily help here as at low speed I'd need torque anyway.
If I was going to change things about I'd want a better tensioning system and may even have to redo the belt guard (vibrating fibreglass thing anyway), so not a minor undertaking.
And if re-machining pulleys, another option is to go to a poly-Vee belt rather than the current A section
Something to think about.
Michael
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25th Dec 2016, 10:08 PM #2Member: Blue and white apron brigade
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Michael I'm finding the graph a bit confusing.
The speed as a number presumably is pulley combo number?
If so, that does not always translate to uniform speed (rpm) intervals between pulley combos.
It would be much more useful if the X axis was plotted as actual RPM then it would show what RPMs you have covered
Next the lines plotted between the points is also confusing because they don't mean anything - its not like it is possible to run at a speed between pulley combo positions X-1, X and X+1.
The torque issue for VFDs can be migrated somewhat by using a vector controlled VFD and doubling the motor size/power.
This will generate at least as much torque between ~12 and 120 Hz as your original motor.
Combine that with a couple of gear combos and you will have all the bases covered plus a much wider range at both ends.
Not cheap but then again it depends how badly you want to generate the optimised speeds.
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25th Dec 2016, 10:21 PM #3Most Valued Member
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Hi Michael, going by your link, is your drill press is a 9 speed?
I just went out and took some pics of my 16 speed plate to see if that's the sort of speeds you're looking for.
16spdcloseup.jpg
DSCF0320.jpg
KrynTo grow old is mandatory, growing up is optional.
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25th Dec 2016, 11:16 PM #4Most Valued Member
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Michael my drill press is similar to Kryn's. Is it possible to fit in an idler pulley? Another advantage is the belts run linearly. I've not heard how well poly-v belts track off axis, but I was always under the impression it was not well, and can jump "v"s. No idea if that's true, but I've seen them jump with tracking faults.
if you really wanted to get fancy you could probably work out a manual variable pulley setup.
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26th Dec 2016, 12:20 AM #5Golden Member
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G'day Michael,
You could set up for optimal speeds in the drill range you use most often and use your mill for larger hole saws when needed.
I assume you are also mapping free spindle speeds, don't forget they will reduce under load with larger drills and hole saws. Unless you are actually having a particular problem I would say don't over think it and go for a pulley setup as per original specs.
If you decide to go with a VFD then vector drives will give better torque at low frequencies as Bob said. Having said that, I use a Sinamics G110 standard drive on a 0.5hp four speed Waldown drill press and have never had a problem operating between 20 and 100Hz. I originally went with the VFD purely as a workaround for the 3~ motor but using the belts to set speed ranges and the VFD to fine tune for a desired speed if necessary is very handy. It also means fewer belt changes in general.
Cheers,
Greg.
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26th Dec 2016, 08:31 AM #6Most Valued Member
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Hi Michael,
my DP does not go below 180 rpm. If I need to use larger hole saws etc. I am forced to use the mill. I assume you have thought about a spring loaded tensioner pulley? That way it can take up any differences in pulley diameter and belt length.
I have looked into enhancing the speeds of my DP but in the end I just can't be bothered. If I was to get to a stage similar to you where I REALLY wanted to do something then I would most likely look at the option of a DC motor and electronic speed control. That way you will still enjoy high torque at low RPM and you won't have to frig around with lots of pulleys, graphs, belt lengths and calculations.
Not sure if I have helped...
Cheers,
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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26th Dec 2016, 08:39 AM #7Philomath in training
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The reason I plotted as a series is that I wanted something to identify points that belong together. The numbers are just the distinct speeds. (This computer is an upgrade, complete with a new version of office and I'm sorry to say that every time MS upgrade they seem to make things harder for experienced users while catering to the people who just want to make a list or pretty picture. I used to know how to change the marker shapes but that sequence of commands seems to have disappeared...)
This plot may be better -
Belt combo2.jpg
The horizontal axis has the target speeds while the vertical are the speeds delivered by the belt combination. The dashed line is the ideal; the dotted line is what is achieved now. Again, lines are to tie a series together and the points represent the exact speeds. Note the gap in speed points on the dotted line. That gap(vertically) between 650rpm and 1800rpm is what I would like to fill
The drill press itself has a 1HP motor on it, so fitting a 2HP motor is not on the cards.
My drill press is similar to Kryn's but 9 speed and has the intermediate pulley set in the middle. To accommodate the slack an idler would be needed but the belts are A series at the moment, so the idler would need to push out. One of the things I like about the poly vees is that the idler can be on the rear of the belt pushing in - potentially much more compact. I have poly vees on the J&S and while they work well enough, there is a tendancy to mis-track. Any pulleys would need to be well positioned so that they don't twist or deflect.
The speeds are based on the motor nameplate rpm. I know that the motor speed will drop depending on load but am aiming for a uniform (logarithmic) distribution with speeds in useful places rather than being bang on a particular speed. Hole saws on the mill are an option except that I like to leave setups there until jobs are finished and I can have several on the go at once (sometimes I even finish them). I also like using larger drills at much lower speeds than 'optimum' if drilling tough materials or the hole is not simple into flat material - so the other day I was cross drilling 10mm holes into alloy steel at around 300rpm. Any more speed and I got chatter etc.
At the moment this is not a firm plan but just a bit of quiet Christmas speculation. I just thought I'd post it for other's thoughts and contemplation.
Michael
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26th Dec 2016, 08:51 AM #8Most Valued Member
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26th Dec 2016, 09:37 AM #9My drill press is similar to Kryn's but 9 speed and has the intermediate pulley set in the middle. To accommodate the slack an idler would be needed but the belts are A series at the moment, so the idler would need to push out. One of the things I like about the poly vees is that the idler can be on the rear of the belt pushing in - potentially much more compact. I have poly vees on the J&S and while they work well enough, there is a tendancy to mis-track. Any pulleys would need to be well positioned so that they don't twist or deflect.
Dean
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26th Dec 2016, 11:16 AM #10Most Valued Member
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There shouldn't be any slack. The centre pully's position floats, so when belt tension is applied it tensions both belts.
1 hp isn't a lot, is it possible to use smaller section belts to achieve a more compact drive arrangement?
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26th Dec 2016, 11:47 AM #11Member: Blue and white apron brigade
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Thanks for positing the new graph.
Is the gap between 650 and 1800 where the belt positions are reversed? I've notice this on a number of DPs
I like to do the same and this is where the VFD comes in useful as often all that needs to reduce the chatter is to slightly drop the rpms - usually a few Hz is all that is needed to do this..
FWIW here is the speed profile on my 16 pulley position DP.
It originally had a 1HP motor and I replaced it with a 1.5HP motor powered by a non VD VFD. This provides at least the same torque as the original motor between 38 and 120 Hz.
The blue dots and associated vertical lines above and below the dots show the full torque speed range.
The red squares show the typical long term usable lower limit (20Hz) for the intermediate and higher speeds where full torque is less of an issue
From belt position ~5 onwards I find I can use frequencies as low as 20Hz (165 RPM) in wood without any problems or overheating the motor.
For metal this is more like position 6.
The drill spends 95% of its time in position 8 (236 - 1400 rpm)
For HD drilling I just change the belt position to position 1, which has full working torque between 120 and 384 RPM
To achieve 3000 rpm requires swapping the belt positions but I don't bother going above position 12 (~1000 to 3200 RPM) while position 16 with its max of 7200 rpm is not really something the drill is designed to do.
The green triangles show the full torque lower limit for a 2x powered VD VFD setup. Position 4 would cover 100 to 1000 rpm. One thing to be aware of is long term use at low frequencies under load may overheat the motor.
RPMsDP.jpg
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26th Dec 2016, 12:00 PM #12Most Valued Member
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Hi Michael, I now understand what you're trying to achieve. I have a similar problem between speeds 683-1166, there is a large jump from one to the other, one is to fast for a certain sized bit while the other is to slow. Whether putting in another set of pulleys, making 4 sets in total, will give the coverage required I don't know. Maths was not a good subject for me, so I don't know how to work out the diameters/speeds required!!!
If you can work out how to fill the gap, I'm interested to do likewise, as I think there would be many others also.
KrynTo grow old is mandatory, growing up is optional.
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26th Dec 2016, 02:00 PM #13Most Valued Member
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just use pulley ratio's Kryn
divide one into the other and divide or multiply as required
ie
driven pulley 100mm
drive pulley 60mm
Drive pulley speed 1400
you can see from the above that the larger pulley spindle must be going slower than drive speed...so if you divide when you should have multiplied you will see its wrong.
100/60=1.6666
therefore 1400/1.66= 840rpm
going the other way
60/100= .6
therefore 1400 X 0.6=840
no need to stuff around with pi or whatever
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26th Dec 2016, 02:17 PM #14Most Valued Member
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Thanks for that Eskimo, So if I have several pulleys, I need to multiply or divide into the next with the previous answer? Just trying to work out to get the speeds to fill to fill the gaps 700 -1100 RPM.
To grow old is mandatory, growing up is optional.
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26th Dec 2016, 08:11 PM #15
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