KNOP lathe DIY build

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KNOP
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Re: KNOP lathe DIY build

Post: # 46727Unread post KNOP
Sat Apr 22, 2017 7:30 am

Hello everyone.

I did some calculations of the cutterhead and figured out that the VTA is about 15° as of now.
Since I am a big fan of the easiest solution, maybe if I added a 10° kink in the torque tube things will sort themselves out and get me a 25° VTA. I think the only problem with this solution is that the drivers and pushrods are at an 10° angle to the cutting angle, but I think this will not lead to differences in positive and negative stroke.
torque tube.png
Anyone who can tell me this is a good plan or not and why?

Best Regards, Wim
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EpicenterBryan
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Re: KNOP lathe DIY build

Post: # 46733Unread post EpicenterBryan
Sat Apr 22, 2017 8:08 pm

Hey KNOP,
I get where you are going with this. The problem is you are still playing around with a printed torque tube (in plastic I assume).
The problem is that at high frequencies there is a lot of acceleration to move mass around. Plastic will flex under such loads. Period. When it does, you have HF roll off no matter what you do. Plastic is just not stiff enough to accelerate mass at high rates. I totally get where you are going with the VCA (vertical cutting angle) but you are chasing ghosts right now. What is really killing you is the plastic torque tube.

Take or leave my comment but there it is... I would concentrate on making (or purchasing and adapting) a metal torque tube. And abandoning using a presto style stylus in favor a much lower mass Neumann 320.

Just my put...

Bryan

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KNOP
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Re: KNOP lathe DIY build

Post: # 46735Unread post KNOP
Sun Apr 23, 2017 9:33 am

Thanks for the pointers EpicenterBryan.

I'm going with an aluminium printed torque tube this time. The 320 stylus will have to wait until another revision, as I do not have any and want to use up my 2 mono cutterhead styli first.
t tube alu v3.png
The rectangular holes are for weight saving / letting the aluminium powder leave the cavity. I hope I receive my print soon.
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EpicenterBryan
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Re: KNOP lathe DIY build

Post: # 46761Unread post EpicenterBryan
Tue Apr 25, 2017 1:41 pm

KNOP wrote:I'm going with an aluminium printed torque tube this time.
Ahh. I missed that.
I don't know about the process or the material. Is it a printed plastic with aluminum powder in it or some other process? Were your other tubes made in the same material or were they plastic?

Bryan

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KNOP
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Re: KNOP lathe DIY build

Post: # 46767Unread post KNOP
Wed Apr 26, 2017 1:07 am

The other torque tubes are in alumide, which is plastics with aluminium powder or something. A bit stiffer than nylon prints, but plastic nonetheless. now I ordered an aluminium print, which is pure aluminium made with the selective laser sintering process. Not cheap, about 40 euro for the tube, so I hope I got the design right the first time. I always order my prints from i.materialise.com. They have an easy to use model uploading service which auto checks for errors, decent pricing, a lot of materials to print and can do priority plastic prints in about 3 days if you need a quick replacement part. Really happy with their service so far.

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sifis1983
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Re: KNOP lathe DIY build

Post: # 46771Unread post sifis1983
Wed Apr 26, 2017 10:38 am

Hi,

Wim, I don't know if the VTA (or VCA) design of your tube, is necessary. Did you align your stylus at 8 degrees, when you cutting?
This is what myshank suggests. I don't know even if other cutting engineers can measure a 25 degree VTA at playback. :roll:

I checked the i.materialise.com yesterday. It seems a great way to experiment with materials for the tube. I will try it, for sure.

At the moment I got this tube for testing:
bronge tube.jpg
The material is brass, but it weighs too much. About 7,5 grams :cry: .

The reason I made a torque tube and V spring like this, is because I want to achieve perfect attachment of the pushrods to the tube, so to avoid resonances that I had with my plastic tube and brass rods.
Anyway, I will try in the next days to see how it reacts.

I look forward to listen the results from your aluminium tube.

Regards,
Sifis
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KNOP
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Re: KNOP lathe DIY build

Post: # 46779Unread post KNOP
Thu Apr 27, 2017 2:17 am

Too bad of the high weight sifis. I'm interested too see how easy the mounting of the drivers to your pushrods will go, I assume you will have the drivers and pushrod/torque tube already installed in the cutterhead before making the connection?
I made an error in the ordered print file, so I made a little changes to the tube and sent them the new file. I undid the angle (with the reasoning that it is easier to asses why exactly the sound has improved/worsened when there are not too many differences between iterations), and trimmed down the model. In theory it should have a mass of 1.05grams.
IMG_20170427_070658.jpg
.
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jjwharris
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Re: KNOP lathe DIY build

Post: # 47074Unread post jjwharris
Thu Jun 08, 2017 11:46 pm

In regards to 3d printing aluminium etc, I'm considering getting in contact with a local jeweler to cast my prints in silver, or possibly aluminium after they have arrived, most likely using the lost wax method.

Has anyone else attempted this and had success?
Record Lathe Embossing Supplies - http://www.supplies.johnnyelectric.co.nz/

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KNOP
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Re: KNOP lathe DIY build

Post: # 47099Unread post KNOP
Mon Jun 12, 2017 1:02 pm

Hi everyone. I've been busy but the cuts are getting better. I made the most progress smoothing out the smaller high q filter points in fabfilter pro above the resonant frequency of the cutterhead. Still not happy with the noise floor however. I hope it is due to my noisy vacuum setup. Got my alu torque tube model and started building a new cutterhead. I hope I can finish the new head by the end of the week.
IMG_20170612_184125.jpg
IMG_20170612_184147.jpg
The alu version weights about 0,35 grams more than the plastic one. I hope that the extra stiffness will compensate for the added moving mass.
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grooveguy
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Re: KNOP lathe DIY build

Post: # 47100Unread post grooveguy
Mon Jun 12, 2017 1:21 pm

Hi, KNOP,

Looks like you're making progress. Be sure to post some results recordings as you go along. One question: how are you anchoring your push rods from the drivers to this piece? I see two holes for the tubes/rods, but do figure on epoxying them in or some other means? Does this assembly simply bolt onto the backplate of your cutterhead, or do the two straps with the holes near the ends actually function as stiff springs, bending (or actually twisting?) a bit with modulation? Nice work.

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KNOP
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Re: KNOP lathe DIY build

Post: # 47171Unread post KNOP
Wed Jun 21, 2017 2:17 pm

grooveguy wrote:Hi, KNOP,

Looks like you're making progress. Be sure to post some results recordings as you go along. One question: how are you anchoring your push rods from the drivers to this piece? I see two holes for the tubes/rods, but do figure on epoxying them in or some other means? Does this assembly simply bolt onto the backplate of your cutterhead, or do the two straps with the holes near the ends actually function as stiff springs, bending (or actually twisting?) a bit with modulation? Nice work.
@Grooveguy
The torque tubes are epoxyed in to the torque tube, and the holes are just for the m3 bolts.

Got the rietschle pump working, measures about 50db of noise at full speed. I will need to see how low I can go. The floor noise of the recordings is down compared to the vacuum setup. Still did not finish the new cutterhead, mostly due to not finding my tools in my mess of a workspace. But I'm almost there.
IMG_20170615_133255.jpg
IMG-20170621-WA0000.jpeg
FB_IMG_1497974155940.jpg
IMG_20170621_122655.jpg
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grooveguy
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Re: KNOP lathe DIY build

Post: # 47172Unread post grooveguy
Wed Jun 21, 2017 2:36 pm

That all looks really good! I do have a couple of academic questions for you, hope you can shed some light.

1) I'm having trouble getting my mind around this vertical tracking angle business. From what I gathered from that article by Keywood, this is only a situation with vertical modulation, the L-R component of the recording. So if no compensation were made, Gladys Knight, panned to center, might sound just fine, but The Pips would be plagued with a bit of second-harmonic distortion. Does this mean that the 'torque tube,' or whatever you call that member in your head running from the stylus to the backplate, needs to be canted at a 15-degree angle? From what I see in the photo, yours looks as if it runs horizontally, or straight back. Maybe I'm misunderstanding this, as Keywood's drawing looks more to do with where the cutter is pivoted than anything to do with the vertical 'moment of force.' If you have a good understanding of this, I'm sure it would help all of us if you could explain.

2) Basic tracking error in even a mono system is blamed on the failure of a pivoted playback arm to maintain a tangential relationship to the groove between the inside and outside of the record. Articles going back to the '40s delve into how to minimize this error by offsetting the cartridge and introducing an 'overhang.' My question is, if the record were cut with a pivoted arm (like the old Presto Y recorder), would such errors tend to cancel (dependent on how similar the mountings were) or would they simply get worse?

Youth wants to know... keep up the good work!

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KNOP
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Re: KNOP lathe DIY build

Post: # 47173Unread post KNOP
Wed Jun 21, 2017 3:11 pm

For question 1: Not an expert so my logic could contain some errors. the vta should be around 15 degrees. This to my knowledge should only affect stereo information, and that is also what I percieve. Tracks with wide stereo panning do sound less good on my cutterhead. But the vertical cutting angle is not the same as the torque tube angle. Its the angle between the imaginary line of the tip of the cutting stylus and the point where the piano wire is fastened, and tge record surface.
Which as of now is around 16 degrees. I intend to cut at an 8 degree angle, totalling to about 24 degrees. There is also the matter of springback of the disc. For laquers i think this is about 20 degree. That means if you were to cut it at 24 degree it would result in an effective 4 degree Cutting angle. As the myshank blanks are stiffer( i think) the springback effect should be less pronounced. But actually i'm going a bit trial and error here. I'm not really concerned with the exact theoretical ways, I just go by ear and see what sounds good and what does not. I am aware that my head geometrycis not optimal, but decides to iterate in small steps as to know why the head sounds better or worse.

For the second question you have the problem that there are a lot of different arm geometries, all with their benefits and downsides. If you would cut in an arc for a specific tonearm it would sound optimal on that exact turntable, but less good on other arm geometries.

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Aussie0zborn
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Re: KNOP lathe DIY build

Post: # 47192Unread post Aussie0zborn
Fri Jun 23, 2017 8:47 am

Good work. No need to worry about swarf catching on fire and exploding.

A few tips on swarf: make sure it gets sucked away. If it sticks to the stylus and forms a ball of spaghetti the stylus heater wires could ignite the swarf and make a mess of your cutterhead.

Put some water in the swarf collection jar in case the flame travels down the suction tube and ignites the large ball of swarf in the jar. I spoke with a former colleague who just happened to be the Chief Engineer at EMI and he recalled an incident involving the swarf jar blowing up.

Here's a video from Aardvark Mastering, USA lighting a large ball of swarf. It's a good party trick that is sure to impress your friends. http://www.aardvarkmastering.com/acetate.htm

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KNOP
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Re: KNOP lathe DIY build

Post: # 47345Unread post KNOP
Thu Jul 13, 2017 8:12 am

Hello everyone,

Finished up the new cutterhead and got some measurements done. Had a lot of work cutting records and fighting with the suction of swarf. The suction worked pretty reliable for a while using the rietschle pump, but now the swarf seems to bowl up almost immediately under the stylus. Perhaps needs to be resharpened?
cutterhead alu.png
The red response is the new alu head, purple the old one with nylon torque tube.
The 100Hz peak is gone due to moving the transformer of the super OEM turntable outside the turntable. I can only recommend this for people using the same table.The main resonance peak has moved up from about 600Hz to 920Hz.
The smaller peak at 3000Hz has remained at about the same frequency, so I will assume this is geometry related.
The peak at about 10000hz has moved up a little, no idea why, perhaps this is a resonance of the stylus?
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KNOP
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Re: KNOP lathe DIY build

Post: # 48075Unread post KNOP
Mon Oct 09, 2017 11:17 am

Hello everyone. Have not had much time to develop the cutterhead, but I'm now building another revision. Most of my spare time I am actually cutting records, and getting the new studio room ready.
I tried to use metal inserts for the threads in the cutterhead this time. I hope this works. Added a 20° angle as well. And the lever thing on the side so I can use a small scale for weight adjustments easily. Added an angle to the suction tube mount, its much easier to bend the alu pipe in the required shape now.
I'm now waiting for extra parts and aluminium 3D prints.I hope to get all the parts by the end of the month, and do some serious testing of the new cutterheads.
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grooveguy
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Re: KNOP lathe DIY build

Post: # 48076Unread post grooveguy
Mon Oct 09, 2017 11:40 am

Remarkable progress, and looks like the 'proper pathway' to some very good results, too. Will feedback flatten-out the resonance peaks, or will you try some simple EQ first? You are indeed an inspiration to us all... good work!

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KNOP
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Re: KNOP lathe DIY build

Post: # 48077Unread post KNOP
Mon Oct 09, 2017 11:47 am

No I would like to know what variables influence what first. I will see how far it can go without feedback, and release the plans for the community and maybe build some as well for others. Would be nice to have an affordable stereo cutterhead option.

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grooveguy
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Re: KNOP lathe DIY build

Post: # 48078Unread post grooveguy
Mon Oct 09, 2017 12:02 pm

Good man! That's the attitude I like, tame the beast in the simplest possible way. A DSP-based equalizer would be the way to go. Analog Devices' "Sigma" DSP platform is a snap to work with and affords a broad range of equalizer and filter 'modules' that can be tuned and tweaked to make ANY curve you need. Their development platform is a snap to use, appearing on your computer screen just like a traditional schematic, or at least block, diagram. The software is free, the chip you'd use (complete with ADCs and DACs) is about $10, but unless you want to learn how to write code, then you'd use their development board (it comes with the chip on board already) and just run it from a PC rather than laying out a board and adding RAM and stuff. The same chip can create things like limiters and, for disc recording, independent HF limiters in addition. And, of course, all the RIAA type of EQ can be part of the picture too.

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EpicenterBryan
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Re: KNOP lathe DIY build

Post: # 48089Unread post EpicenterBryan
Mon Oct 09, 2017 8:23 pm

grooveguy wrote:Analog Devices' "Sigma" DSP platform is a snap to work with...
Jim, stop it!
You sent me on a three hour (de)tour, a three hour (de)tour.
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Bryan
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