Feed Screw Project (Presto 6N, 8N)

Post: # 21316Unread post **MBL** Mon Oct 08, 2012 12:16 pm

Ok so I have been thinking more and more about feed screw needs. These things seem to be frequently missing. I do have a good machine shop that I can work done at. Mark from the forum was gracious enough to send me a technical drawing of a feed screw that will be helpful.

Now, I don't know what it will cost as of yet, but I think it would be good to get a poll of what screws are most useful and how many might be needed by forum members.

It would even be better if someone might be willing to lend a feed screw for the cause. I know I read that a 112LPI screw came with the 6N, but what other screws would be useful any why?

Thanks for any thoughts on this. Before long, I should be able to figure out a price on each piece from the local shop.
Tim
MBL

Post: # 21317Unread post **piaptk** Mon Oct 08, 2012 1:11 pm

I had some feedscrews made up in the past. They were all 180 lpi, because between 160-190 is the sweet spot for fitting a good amouint of music on a disc at a reasonable volume... about 190, you have to start watching volume and bass, and below 160, you have to cut very short records.

I just looked into getting some more made, and they were going to cost me even more than last time, and it was pushing $100 a screw (with a minimum of ten), which is kind of ridiculous. My friend and I are shopping around right now for a shop that can do it cheaper.

I would say that for simplicity sake (each lpi requires a seperate design for the machine), I would make 128, 180, and 224. That should cover anyone's needs.

Also, be sure to make them out of stainless steel. Some of the screws I had made last time got rusty if left in a damp environment.

Depending on the price, I'd be a buyer for some screws.

Post: # 21318Unread post **MBL** Mon Oct 08, 2012 1:16 pm

Aha! Some interest! Ok thanks for the input. I understand from Mark that the more lines, the shallower the threads need to be. The LPI is associated with the record itself right...not the screw itself...So wouldn't I need to know the thread pitch for each LPI?
Tim

Post: # 21319Unread post **MBL** Mon Oct 08, 2012 2:01 pm

So I was looking at the Presto 6N manual and it said that feedscrews were available in 96, 112, and 120 LPI... this seems to be dreadfully short...no? At 78 RPM how much time would you have on one side of a record...say 10"
Tim
MBL

Post: # 21322Unread post **tragwag** Mon Oct 08, 2012 3:02 pm

this thread answers your LPI questions
https://lathetrolls.com/viewtopic.php?t=824.html

I've been looking into more feedscrews, now that I have two lathes operating at once.
I'm in talks with a machine shop, I'll let you know the results.

Post: # 21325Unread post **MBL** Mon Oct 08, 2012 5:46 pm

So between this thread...the link provided and friendly forum member Mark R...I am getting close to knowing the info I think I need. Now what is it I need to ask the machinist? Do I. Need to provide a specific thread pitch, and if so, do we have a thread pitch to LPI table?
Tim
MBL

Post: # 21327Unread post **markrob** Mon Oct 08, 2012 7:57 pm

Hi,

If you look at the drawing, you'll see the ratio is 8:1. So a 112 LPI feedscrew is cut 14 threads per inch.

Mark

Post: # 21330Unread post **Angus McCarthy** Mon Oct 08, 2012 9:35 pm

Also, count me in if you get a batch to sell. I've got naught but a lowly 112 at the moment.

Post: # 21335Unread post **Steve E.** Mon Oct 08, 2012 11:22 pm

I had a very reliable guy all lined up to do this a couple years ago (for the Presto 6N) and it fell apart because I couldn't get a minimum order together (10 minimum was needed). If there is enough interest, I can get my guy to plow ahead. But if you have someone too, we can see.

I do have some lower gauge 6N screws, too, all ready to sell. out to in, in to out. I was too preoccupied to sell them before. I'm in a better place to do so now.

I'd be interested in getting some VERY low gauge ones made, for puzzle records. 24 lpi, etc.

I can never remember whether the highest I've used is 224 or 240. (It's stated in some other threads around here.) Whichever it is, I have had perfectly decent results, albeit a little quiet. I'd personally like to get several made up for myself between 180 and 216. I want to make LPs.

Post: # 21338Unread post **MBL** Tue Oct 09, 2012 5:43 am

Well I have the drawing on its way to the machine shop...a buddy of mine is going to swing by there in a bit. Then I will have a better idea of the price range. To start, I wouldn't mind having some of the standard values like the 112. A 128 would be good too.
Tim
MBL

Post: # 21340Unread post **markrob** Tue Oct 09, 2012 7:57 am

Hi,

If possible, try to get an actual feedscrew to send to the shop. A real machinist will probably see details that I did not see. I'd also have one done as a first article sample before doing a bunch and finding issues.

Mark

Post: # 21341Unread post **MBL** Tue Oct 09, 2012 8:09 am

It certainly would be best to have at least one sample, but I hesitate to ask someone to lend a screw for the effort. Simply because they would need to be trustful enough to do it and I could understand how someone would be weary of it.
Tim
MBL

Post: # 21347Unread post **petermontg** Tue Oct 09, 2012 10:05 am

Check with machinist how he will mahcine the threads, they have to be CNC'ed. If done by hand the threads will wear faster. Also make sure the machinist can do your desired LPI. My guy can't hit certain LPI but he gets as close as possible maybe -1/2 LPI. You need to bring your maths with you so he can understand how you calculate LPI and break it down so his cnc can understand what to do.

Post: # 21350Unread post **Steve E.** Tue Oct 09, 2012 12:30 pm

My machinist creates stuff for medical equipment. He is apparently the man. MBL, let's chat to make sure we are not at cross-purposes.

Post: # 21351Unread post **markrob** Tue Oct 09, 2012 1:32 pm

petermontg wrote:Check with machinist how he will mahcine the threads, they have to be CNC'ed. If done by hand the threads will wear faster. Also make sure the machinist can do your desired LPI. My guy can't hit certain LPI but he gets as close as possible maybe -1/2 LPI. You need to bring your maths with you so he can understand how you calculate LPI and break it down so his cnc can understand what to do.

Hi,

I don't see any reason the screws need to be CNC machined. The original Presto screws sure weren't. The wear factor should have more to do with the materials used. In the case of the Presto screws the knife edge is supposed to be the wear item. When I made mine, I used free machining 12L14 steel as its easy to work with on a small bench lathe. I did not attempt to heat treat the screw to harden it, but I could see that using oil or water hardening drill rod might be a good idea.

That said, once setup, CNC would be a great idea if you were making a number of them. I could see most of the operations being done in one setup.

Mark

Mark

Post: # 21382Unread post **Steve E.** Wed Oct 10, 2012 8:22 pm

I just updated this thread:

https://lathetrolls.com/viewtopic.php?t=824.html

It now has more running times and it should be easier to read. It has some VERY low LPIs in case anyone wants to make puzzle records (parallel grooves).

I am going to put a call into my medical-machinist friend from a couple years ago, make sure he is still on board with cutting some feed screws, and get a quote from him. I'm going to get some screws cut for myself.

If people PM me again ASAP with the screws they are interested in buying, I will put together a quote and get back to you to see if you want to move forward. Basically, because of the way his process works, I can do this in lots of 10. I'd love to give him an order of either 10 or 20 screws.

I can't guarantee that my prices will be as low as some local machinist of yours. But my guy has a great reputation, and if you don't want to hassle with getting your own machinist, this might be worthwhile for you.

In case you are curious....As for me, I have a decent run of feed screws already. I actually use my 240 LPI screw a LOT, my 256 sometimes, and I find myself wishing that I had a run of several screws between 192 and 232. This is because I want to cram as much running time on an LP side as possible, and minimize the compromise each time. In addition, I will be making a 24 LPI and 48 LPI for puzzle records.

Let me know.

Post: # 21559Unread post **Steve E.** Mon Oct 22, 2012 6:11 pm

OK! I have 13 tentative 6N feed screw orders. Nobody is committed until I after I confirm the price, but this will help me get an estimate.

Requests include LPIs of:

24 (for puzzle records)
48 (for puzzle records)
176, 180 or 184 (I will probably just pick one of these three gauges)
192
208
224
240 or 256 (I will probably do 240)

Please PM me if you want in on the order. Unless I there are specific requests, I will most likely fill out the order with extras of the 180ish, 224 and 240.

Post: # 21561Unread post **dietrich10** Tue Oct 23, 2012 7:11 am

Post: # 21563Unread post **Steve E.** Tue Oct 23, 2012 1:44 pm

Confirmation from my machinist! I am going to visit him in the next week and get a new estimate.

Post: # 21567Unread post **Steve E.** Tue Oct 23, 2012 4:36 pm

Two caveats emptor, by the way:

1) If you have not altered the blade that rests on the feed screw, you may have problems with higher LPIs (not sure of the cutoff). My blade was modified somewhere along the line, such that the edge is flat on the "out" side and tapered/angled on the "in" side. Alan Graves recommends replacing the blade with a reshaped X-acto blade if need be.

2) The 24 and 48 LPIs have never been tried before, and I don't even know if they are possible to manufacture or if they will work. It may be that the grooves in the screws will have to be impossibly deep if the blade is going to track them. It is also possible that there will be too much resistance in the cutterhead assembly for it to move that quickly. I intend to try an experiment with those gauges before making a bunch of them.