What Zero Height Setter?

[Jasonb]

Andrew's recent mention of setting tool heights has prompted me to ask what members suggest as a suitable height setter for my CNC.

At the moment I'm just using the 20mm side of a 10-20-40 block and jogging down until they won't slip under the tool but would prefer something a bit better than that. I don't have any quick change tooling so break the program down into sections for each tool, run that then load the next code and change tool.

I don't feel I need one that wires into the machine so just one of the blocks or cylinders with a dial or digital readout, I'm thinking the dial is easier to see what's happening rather than counting down on a digital one. Also as most of my items are quiet small I'd like the setter to be the same so a 50mm height one with a smallish footprint.

Any suggestions?

J

[Vixen]

I made this elephants foot tool height setting dial a while ago. The photo below, should be self expiatory. I find it is useful for measuring the tool offsets for a rack of tools. The individual tool offsets are entered in the tool table. The CNC controller compensates for the individual offsets as each tool change is called and loaded into the quick changer.



For single tool setting, I still prefer to touch off onto a thin strip of typing paper. I jog down in 0.001" (or metric equivalent) steps until the tool just nips the paper. Set zero and lift the tool and your ready to roll.

Mike

[steamer]

I have the Tormach height gage and special granite plate for setting tool heights individually.   Though I think setting it on the machine is a better idea in a small crowded shop

Dave

[steamer]

Having a usb link from the tool setter to the control is nice...eliminates typos.   The Tormach tool setter will do this

[kvom]

I use a 1" gauge block, but only jog upwards until it slips under the tool.

[Admiral_dk]

There are a number off cheap (not always sold at a cheap price) Height Setters out there. They are basically a  simple switch that has a reasonable accurate (not from switch to switch, but from test to test with same switch) point and a good long service life. Most CNC Control programs (LinuxCNC etc.) has an option to connect them together. The program will slowly 'Plunge' the Mill-Bit down until it triggers the switch and then even slower rise it again until the switch is inactive - this point will be the Zero Height !!!
I've seen a few programs do it a few times very shortly after each other - I do not know if it just confirms or do an average to improve the resolution of the switch.

I have discovered a problem with this approach when the diameter of the mill bit increases - you might either not have the lowest point off the mill bit / head be the part the touches the switch or it might press the switch at a slight angle that changes the switch point.

All this can be improved by making the whole system yourself on the lathe. First make a rough 'plate' bigger in diameter than you biggest milling head. Attach a straight precision axle to it - in such a way that it can't go loose !!!
Then hold the axle in the lathe - probably best option would be in a collet - and remove enough from the 'top' to ensure a very flat, smooth and perpendicular surface to the axle. Optimal end result off this part, should be stiff and light - the later can (and probably should) be helped with an assist spring.
Now make a Base with a flat bottom and options for securing it to the mill bed, that has space inside for the switch and two wires out + a straight perpendicular hole for the axle.

I hope this might be useful 

Per

[Hugh Currin]

I do this with a machined 1" piece of aluminum. Will have to pop for a real gauge block one of these days. I generally move the tool too low, jog up 0.005" increments till the block slides under tool, then jog down by 0.001" until I can just slide the block under the tool. This to counter backlash. But, as kvom says, don't jog down while block is under the tool. The machine will use every bit of force it can muster to force the tool that last 0.001" into the block. Bad bad.

I have Tormach quick change tooling and really like it. My set came with a small granite setting stand that I have yet to use.

Will be interested in what you come up with. Thanks.

I use a 1" gauge block, but only jog upwards until it slips under the tool.

[Dave Otto]

I just use a spare .1" gauge block. At work I have a nice 2" spring loaded checker with an LED indicator that works quite nice.
My home machine is a converted knee mill with limited Z travel so any type of height setter takes up precious space.

Dave

[cheepo45]

I use a .001 feeler gauge and a block.
Just move it down until it grabs the feeler, nd add .001 to the block for your Z setting.
 Scott

[Dan Rowe]

I have a pack of rolling papers in top of my machinist box. They measure .001" tear off a strip and hold it lightly and when it grabs set the dial.

Cheers Dan

[Jasonb]

Thanks for all the replies, it seems like what I'm doing already is not a lot different to what the rest of you use so maybe I'll just stick with that.

Vixen's one with the dial looks to be the closest to what I was thinking off but a bit bulky for setting individual tools and Dave's light up one would be a similar shape but I think I would prefer a dial to see how far to jog if I did buy something.

keep the ideas coming.

[Vixen]

There is always these, from China. They come with their own make-up box!!

These setters are 50mm tall. My 'home made' dial setter is currently 32mm tall but could easily be remade to 25mm (or less)

https://www.ebay.co.uk/itm/Z-Axis-Setter-Magnetic-Measuring-Tool-Pre-Setter-50mm-for-CNC-Router-Machine/283250188028?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D228435%26meid%3D33b8d387ff8440d59ac98a36e88d0fb4%26pid%3D100005%26rk%3D3%26rkt%3D12%26mehot%3Dpf%26sd%3D173528747532%26itm%3D283250188028%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithoutBoostBBEV1&_trksid=p2047675.c100005.m1851

Mike

[Jasonb]

Yes those were the type of thing I had in mind, just wondered if anyone may have used one and if the repeatability was OK.

I've got plenty of height but as I often use the top of the part as my Zero want a smallish base area, yours looks quite large and not that balanced unless on a nice flat surface.

[Muzzer]

Check out Cluff's video on the subject:
<a href="https://www.youtube.com/watch?v=wDGvQHevN9Y" target="_blank">http://www.youtube.com/watch?v=wDGvQHevN9Y</a>

[Jasonb]

Thank's Murray, good video and seems like the dial type is the way to go. I've not seen his videos before so will have a look through them over the weekend.

J

[jadge]

There's a difference between setting tool offsets and work zero setting. I used to faff about with fag papers and touching off tools. But I got fed up chipping carbide cutters and it gets "exciting" if one forgets to enter a tool offset.

This is what I do now, starting from scratch:

1. I make tool 0 my master tool - simply a length of silver steel with a rounded end that is longer than any tool I'm likely to use. After power up and referencing I set Z=0 using the master tool on the mill table as indicated by a fag paper.

2. I got so fed up with manual tool setting that I bought an electronic tool setter. This plugs directly into the mill. After checking that it works (red LED on the unit and the screen) I set the tool number to 1, insert tool 1 and move it so it is just above the tool setter. Then, on the offsets page, I click the set tool offset button and the machine automatically moves the tool down to trigger the setter and then automatically inserts the result into the tool table. The result is the difference in length between the master tool and the tool being measured. Since everything is automated the machine also takes into account the height of the tool setter. The sequence is repeated for each tool in the set.

3. Once the tool offsets are set I can concentrate on work offsets. These are determined in the CAM program. Although I sometimes use the work itself I normally use a fixed reference such as the vice jaws or a hole drilled in an appropriate place in a temporary plate that holds the work. I use a Haimer edge finder and/or a Haimer Centro (coaxial indicator) to set X and Y zeros.

4. The Z work zero is set using the master tool against whatever plane I have set in CAM using the time honoured fag paper. Sometimes I use the top of the work but more often use the temporary plate on which the work is mounted, or the mill table itself for work direclly mounted on the table.

It sounds involved but one can rattle though quite quickly. When using the normal spindle I have the Tormach tooling system so height of the tool when fitted is consistent. I use a post-processor that incorporates the use of the tool table at tool changes.

The high speed spindle holds tools directly in an ER11 collet, so there's no repeatability on tool offsets. When using it I go straight to setting the X and Y work offsets. I set the Z work offset by adjusting the tool so that a known gauge block (usually 10mm) will slide under with some drag. The Z height is then set to 10mm. I generate the G-code using a post-processor that does not invoke the tool table to adjust tool length.

Andrew

[rklopp]

Check out Cluff's video on the subject:
<a href="https://www.youtube.com/watch?v=wDGvQHevN9Y" target="_blank">http://www.youtube.com/watch?v=wDGvQHevN9Y</a>

I use the blue version (from Shars) on a Haas TM-1. It is OK, but can stick occasionally. I have a Lyndex one that works on the same principle, but fit and finish is nicer and it is square and parallel ground on all but one face. It even has a foot that you can hook over the back of a vise jaw if you are measuring a horizontal spindle.

Using the Shars setter, the tools are all at Z = 0 on a plane 2.000 in above the table. The part Z-zero offsets are the distance from this plane to the part Z = 0.

I use the Lyndex setter on my Deckel CNC, which does not have tool management like on a Haas. I use the Lyndex together with a Haimer Taster mechanical probe. The Haimer is my "0" tool. I set it to -0.1969" (-5.000 mm) on the shoulder of the Lyndex, which is 5.000 mm below the plunger face when it is at 0.000. Then, I read the Z value for each tool using the plunger. Those are my tool length offsets that get written down entered manually into the tool table on the Deckel's control. When I am ready to run a part, I set machine Z=0 by probing the top face (or whatever face I want to use) with the Taster and punching in the Z value it is supposed to be in the g-code. I can use the same tool length offsets over and over in any program, and just have to re-probe with my Haimer "0" tool when I run a new part.

[Doc]

I designed and built an electronic height setter for setting my tools. Here is a video o fit.


<a href="https://www.youtube.com/watch?v=lUdjfhKke5U" target="_blank">http://www.youtube.com/watch?v=lUdjfhKke5U</a>

[awake]

I made this elephants foot tool height setting dial a while ago. The photo below, should be self expiatory. I find it is useful for measuring the tool offsets for a rack of tools. The individual tool offsets are entered in the tool table. The CNC controller compensates for the individual offsets as each tool change is called and loaded into the quick changer.



For single tool setting, I still prefer to touch off onto a thin strip of typing paper. I jog down in 0.001" (or metric equivalent) steps until the tool just nips the paper. Set zero and lift the tool and your ready to roll.

Mike

Mike, that is a great idea!

[Jasonb]

Thank's for the input Andrew though I think only the last paragraph will apply to me due to not having a tool change system and is not far removed from what I do now.

Doc that looks a neat size, will have a watch of the whole video a bit later.

[jadge]

Depends on your spindle taper; if it's R8 you can use the same system. I use the same special R8 collet and holders on the Bridgeport for most general machining. I'm not sure I call it a tool change system per se, more a means of ensuring repeatable location of tools so that pre-measured tool offsets can be used in a tool table.

Andrew

[Jasonb]

Yes I was looking at the Tormach site a couple of days ago and see it's R8 which would fit the KX3 and SX2.7 I was prompted to visit by a video of a lever action drawbar and TTS fitted to a SX2.7 that came up on Youtube.

Although it's not that expensive (unless you buy lots of holders) and i could afford it for the couple of times a month that I may use the KX3 it's hard to justify the outlay particularly as most things are one offs so may have to use specific cutters that would need setting anyway. I practice would expect you keep commonly used cutters in their own holder all the time and just have some additional holders for job specific cutters once you get into it.

it would have been handy on something like that batch of 12 spokes where I ended up using one cutter and swapping workpieces in the vice before running the next cutters code and and again changing the work rather than tool

[steamer]

The TTS system isn't bad....  it has its limitations at higher power levels, but on the 440 it seems fine

Dave

[Vixen]

Any quick change or lever action tool changer is worthless unless you invest in lots of tool holders. Thats were the money adds up.

Here is a useful tip. If you decide to buy a load of tool holders from China, break the order down into two at a time, otherwise the 'Customs and Excise' get very excited at the weight of the package and the less than truthful customs declaration label your seller will have added.

Mike

[Doc]

Doc that looks a neat size, will have a watch of the whole video a bit later.

It is  exactly 1.000 made it to that because I set my clearance plain in NC programs to 1.000 so I can change tools quickly and go to clearance plain and set my tool. I have drawings for it and it is quite easy to make.

[steamer]

Any quick change or lever action tool changer is worthless unless you invest in lots of tool holders. Thats were the money adds up.

Here is a useful tip. If you decide to buy a load of tool holders from China, break the order down into two at a time, otherwise the 'Customs and Excise' get very excited at the weight of the package and the less than truthful customs declaration label your seller will have added.

Mike

I don't know....Not subjecting my not NEARLY new rotator cuff to a draw bar wrench putting on and off every tool change is kinda nice with just a push button away..........just sayin.   If it hadn't already come with the mill, I'd a spent the 400 bucks to put it on.  I have 12 holders currently...

Dave

[awake]

I designed and built an electronic height setter for setting my tools. Here is a video o fit.


<a href="https://www.youtube.com/watch?v=lUdjfhKke5U" target="_blank">http://www.youtube.com/watch?v=lUdjfhKke5U</a>

Thanks, Doc - nice little project!

[Hugh Currin]

Jason:

I have and use the TTS. However, my use is pretty much as a Neanderthal. I don't keep a set tool table nor keep set tooling in specific holders. I also set tool offsets from machine Z zero, which is the highest travel in Z. This does a couple of things for me. Not keeping a set tool table means I don't have to be super organized using a tool rack. Depending on it and getting a tool out of place would be disastrous. Keeping set tooling would also lead quickly to a lot of tool holders.

Keeping Z=0 at machine Z zero and setting tool offsets from there prevents crashes for me. Setting Z=0, for example, with the spindle face on top of the vice, and then defining offsets from there causes trouble for me. If the controller thinks no tool in mounted, but one is in the spindle, a move to Z=0 would drive the tool into the vice. Note, without a tool changer the machine is depending on me to mount the right tool, or lack there of. With my knee mill keeping a tool table of offsets from machine Z zero does little good, it changes each time the knee is moved.

The TTS is a real advantage to me though. I set up tooling and offsets for a particular job and layout the tools in order. It helps with one off parts, but the real advantage is making more than one. The TTS gives a consistent tool length upon changes making this all possible. As a hobby the extra time (at ten cents an hour?) in setting tools for each job just isn't a problem.

As I said, a Neanderthal approach. If speed mattered I'd have to change my ways, but for now no need.

Stay safe.

[Art K]

I just caught this. I sometimes jog down then scroll down in .0001" increments till my Dorn hardware recept drags, then set the z height to .002". My new favorite is to use an adjustable parallel. Set the tool above the part, slide the ends together snug up the screw push Z zero raise the axis pull out the parallel, run the axis back to z zero then type in the dimension from the micrometer.
Art

[Jasonb]

Doc, I watched the video and may have a go at making one, your explanation is enough to see whats needed. I wonder if making the top insulator from clear material would allow the LED to be placed inside to give a ring of light around the plunger that would be bright enough to see?

Thinking about my own use with a TTS 10 holders would seem to be a practical starting point as there are 6 or so cutters that tend to get used regularly and that would leave the other 4 for any job specific cutters. Just need to talk Ketan into stocking a similar system and sending me some to test

Dave brings up the point about air, although the TTS looks like it will work with a manual drawbar an air powered one would be nice in which case I would also need to up my compressor size which I need to do anyway if i'm going to run some form of fog buster which would be handy for cutting aluminium, rest can be done dry but the air for chip clearing would come in handy.

[Muzzer]

With my knee mill keeping a tool table of offsets from machine Z zero does little good, it changes each time the knee is moved.

...which is why the offsets are usually defined as the difference between the current tool and a reference tool. That way, when you change the height of your table / knee, all you have to do is remeasure the "Zref" value (machine coordinate of the ref tool), then all the other offsets are still valid. When you have a decent number of tools, the last thing you want is to have to remeasure the whole lot each time you move the knee.

If you want a "failsafe" system, you might choose a long ref tool and default to zero for the tool length offsets. Then if you forget to change a tool's offset from zero the spindle will stay near the top of travel - but you will still have valid offsets for existing tools.
 
If (like me) you have a knee mill, you might find this into quite useful http://www.cncsnw.com/OLEM.htm, particularly the illustrated guide linked near the beginning. Some of this stuff takes a bit of getting used to, despite being fairly simple on the face of it.

[Doc]

Doc, I watched the video and may have a go at making one, your explanation is enough to see whats needed. I wonder if making the top insulator from clear material would allow the LED to be placed inside to give a ring of light around the plunger that would be bright enough to see?

I'm betting it would that's a neat idea!

[Dave Otto]

This has been a very interesting thread; I also have a knee mill and was hoping some of the knee mill guys would chime in, Hugh, Murry, and maybe Doc.

I do what works for me but there may be better solutions when it come to managing tool heights in Mach.  I set every tool for each job and set the top of the part with the last tool; this gives me consistent results but depending on the number of tools this can take a while.
I have never tried the master tool approach because I couldn't wrap my head around it. I use the Mach Standard Mill screen set form Calypso Ventures which I quite like. When I was first getting going with it I had asked for clarification via his user forum and he pretty much told me that if I can't understand his instructions that I should purchase a CNC text book and start reading. I was just trying to figure out the moving target of the knee mill.
My machine at work I keep a standard set of tools loaded and all set from my fixture plate. Makes it quick to program when most of the tools that you need are already in the machine and set.

Anyway thanks Murry for posting the link, I will study that information and see if this old dog can learn something new.
Jason,  I have collected quite an assortment of TTS tool holders and generally I'm pleased with the performance and convenience of them. I have my drill chucks mounted on TTS holder but do to the quill travel limitations I most often put my drills in ER holders; this keeps everything about the same length. I think that you would be happy with them if you added them to your tooling options.
Having the ability to set all your tools at the beginning of the job and not have to set each tool during the tool change is a huge plus.

Just some of my ramblings,
Dave

[Dave Otto]

http://www.cncsnw.com/OLEM.htm#Methods
Procedure #2 is what I have been using.

Dave

[Hugh Currin]

Dave: I think I'm also using Procedure 2, as noted at the bottom setting tools for each job.

Muzzer: A long reference tool might work for me, I'd not thought of this. The web page you referenced even suggested this, "Centroid has traditionally recommended that your reference tool be longer than any other tool." I'll have to make up a long reference tool and see how the process works, for me, in LinuxCNC. It would be a change in shop culture, but that's happened before. :-)

Thanks.

[jadge]

My master tool 0 is the one on the left:



When I upgraded from Mach3 to PathPilot Tormach reckoned I should use the spindle nose as a reference rather than a master tool. I told them I disagreed with them then, and I still do. Using the spindle nose may be the professional way, but for me it would be a pain. It's difficult to see what's going on, especially if you need to probe on a point that is below the vice jaws for instance.

I would disagree that one needs lots of toolholders to make a quick changer worthwhile. I don't have many toolholders but it works fine for me. I keep 10mm and 6mm endmills permanently in holders. I also have spare 10mm and 6mm holders, plus 3 ER collet chucks and four drill chucks on tapered holders, one small chuck, two medium and one large. I've never used the imperial holders I bought to start with. I use metric cutters for most machining. The imperial cutters I use for keyways and counterbores are threaded so I use an Autolock chuck.

I bought a power drawbar kit from Tormach a long while back. Really must get around to fitting it.

One of things that drove me to use a height setter and tool tables was that I found I was only using one tool per program and swapping work several times if multiple tools were needed. That became a right royal PITA pretty quickly.

On the CNC mill I tend to run fairly small tools at high spindle speeds and feedrates. But I've given the TTS system a run for its money on the Bridgeport and never had one come loose on the Bridgeport. I wouldn't want to run it at more that 1.5hp available on the Bridgeport; but the same would go for the R8 taper.

Andrew

[Hugh Currin]

Thinking through using a reference tool I came up with a downside. There are two touch offs required, one for the reference tool and one for each tool. So if there is any error in touching off that error is doubled. I can't think of a situation I've had that this would matter, but it's there.

Andrew: If it was my comments, I was not saying quick change tooling leads to the need for a lot of tool holders. Rather I thought that keeping tools permanently in individual tool holders and in a tool table could. I find the TTS system I have a great help without keeping a permanent tool table. With it I change tools rather than change parts.

P.S. You guys got me looking around again. I ordered a 1" gauge block from ebay for tool setting. Should be here next week.

Thanks.

[Muzzer]

Just to complicate matters, my reference tool is also my touch probe. It's a Renishaw probe that is miles more accurate than my machine will ever be but it is relatively long for what it's worth, so the other tools tend to be shorter. I can acquire the "Zref" value for the current knee / table height using the probe to touch off on the tool setter. Then use the same probe to find the X, Y and Z coordinates of the workpiece. Dead handy - and deadly repeatable.

I have to admit I often / usually load any new tools and check that the tool length offsets appear to make sense before running a job. For this, you activate the tool length of the current tool by running G43 Hx in MDI, where x is the tool number. This should adjust the current WCS (G54 etc) to suit the new tool offset (the displayed value of the G54 Z coordinate should change to suit the new tool). If I then jog down to just below Z10, I should find a 10mm diameter tool shank will just roll under it as I slowly jog back up past Z10.

If you have a bed mill (such as the Tormach), your Zref should always be at the same machine z coordinate (height) for your ref tool. This simplifies the sums. Conversely, if you have a turret / knee mill and are given a tool length setting macro, be aware that it may not take account of the variable knee / table height. This caused me some grief on my other knee mill and I ended up having to write my own macros.

[steamer]

Doc, I watched the video and may have a go at making one, your explanation is enough to see whats needed. I wonder if making the top insulator from clear material would allow the LED to be placed inside to give a ring of light around the plunger that would be bright enough to see?

Thinking about my own use with a TTS 10 holders would seem to be a practical starting point as there are 6 or so cutters that tend to get used regularly and that would leave the other 4 for any job specific cutters. Just need to talk Ketan into stocking a similar system and sending me some to test

Dave brings up the point about air, although the TTS looks like it will work with a manual drawbar an air powered one would be nice in which case I would also need to up my compressor size which I need to do anyway if i'm going to run some form of fog buster which would be handy for cutting aluminium, rest can be done dry but the air for chip clearing would come in handy.

My little California Air compressor works great and is single phase....and handles the fog buster and the draw bar just fine.

I think it's about 4.4 cfm

https://www.amazon.com/California-Air-Tools-CAT-4620AC-Compressor/dp/B005SOD08M/ref=sr_1_6?crid=1985S0C081AQN&dchild=1&keywords=california+air+compressor&qid=1598218867&sprefix=california+air+%2Caps%2C176&sr=8-6


Dave

[Doc]

Well this thread got me going again on wanting a quick change and some tool holders. So I finally pulled the trigger and ordered a set. I have been just running one tool at a time. That is what drove me to a quick and easy way of height setting and constructing the 1 inch tool setter. I'd pot the too; in and move knee up to the setter and then ready to go. Works fine if you only run one part at a time but I usually run at least 2. So now I'll be able to set the tools up and run as many parts as I want at a time. Been wanting to do this since day one with my N/C machine.

[Jasonb]

My little California Air compressor works great ..........................

Mine is half the power, half the tank capacity, probably half the CFM as they only quote displacement not delivery and at 94db considerably louder and at 30yrs old showing it's age a bit hence I would want to upgrade.

[Muzzer]

I have a tiny Bambi compressor. It's less than 2 cfm (50 l/min) but it's only operating the power drawbar and gear selectors on the machine. I also use it to give little blasts with a nozzle for clearing chips and coolant to avoid recutting (= broken tools). It's also nearly silent (40dBA) , sounding more like a fridge than a lawnmower.

[steamer]

My little California Air compressor works great ..........................

Mine is half the power, half the tank capacity, probably half the CFM as they only quote displacement not delivery and at 94db considerably louder and at 30yrs old showing it's age a bit hence I would want to upgrade.

Would recommend the California Air unit.    That's an Amazon link...and is the cheapest source I've found for that unit.   They have a unit that is 1 step up from that, but it's 220 single phase...and a good deal larger current wise than any 220 line I want to dedicate to it   ( I have 220 1 phase 60 amp line in the shop, but it's running my big lathe at the moment...)

Dave

[steamer]

Jason...94db is physically exhausting to listen to...to say nothing of harmful to your ears.    This unit is truly a 60 db and is no trouble to have "kick on" while having a phone conversation with someone.    It was worth it to me anyway!

Dave

[awake]

Doc, I watched the video and may have a go at making one, your explanation is enough to see whats needed. I wonder if making the top insulator from clear material would allow the LED to be placed inside to give a ring of light around the plunger that would be bright enough to see?

I'm betting it would that's a neat idea!

Yes, great idea!

[dieselpilot]

The California Air Tools compressors are pretty good even if they are 70dB not 60.  I have a 10200C and added an aftercooler and water separator. It ran about 50% duty cycle when in use and made fairly dry air until the tank warmed up. The biggest disappointment is the unloader valve isn't silenced. I fixed it with a solenoid valve and silencer, bypassing the valve in the pressure switch. It is now a backup after upgrading.

[Jasonb]

Anything will be better than mine! and with sound level being logrithmic if I remember rightly even 10dB will be half the volume. Unless the cutter is making noise I can hardly hear the mill running outside the workshop door so it would be nice to keep it that way if a fog buster is running as that will mean the compressor comes on far more than with the odd manual squirt of air that I have been using at the moment.

Looking around it seems like the displacement being quoted rather than delivery volume sound levels can be used to the sellers advantage too. Some quote the noise on initial startup from an empty tank while others when just topping up with this being a lower level. Then some state the distance from the machine and others don't. There seem to be some reasonably priced 7-8cfm ones with 50lts tanks about in the 65dB range so may look at those.