Gear Ratio With Pitch Feed Rate

Anna Jablonska	04/09/2011 10:58:17
14 forum posts 1 photos	Dear All., Perhaps it is just one of those days, but I've been unsuccesful in resolving an issue - so am turning to you for some advice. What I would like to understand, is how to calculate feed rates on the Myford, when using a gearbox set up for metric screw cutting. Eg. Assume I have set up to cut a metric thread of say 1mm pitch. Using of course the change wheels / quadrant & gearbox. If I now want to leave the set up in place, but perhaps need a different feed rate how could I define / calculate to where I should reposition the gear selector or the three position lever ? Looking forward to any replies. Kindest Anna
Roderick Jenkins	04/09/2011 12:48:12
2233 forum posts 687 photos	Anna, I've been investigating this with a view to using the gearbox/changewheel combination to produce some long leads for helical gears. My understanding is that the set up gives 2 ratios, one for the gearbox setting and one for the changewheels. When the set up for screw cutting is in imperial mode the gear ratio (from mandrel to gearbox input shaft ) is 1:1 and the gear box in effect gives you a variable pitch leadscrew, 8tpi, 9tpi etc to 56tpi. With the metric quadrant in place then you can work out the gear ratio from drivers / drivens and then divide by the gearbox setting as if it was the leadscrew tpi to give you the lead. For example: from the metric conversion chart, the gear settings for 0.2mm pitch are: 28/60, 63/50, 45/60 = 0.441. If you now set the gearbox to position C8 for 56 threads per inch you get a feed or lead of 0.441/56 =0.008" per rev. If you multiply that by 25.4 you end up with 0.2mm, as from the chart. To get a finer feed you will need to make the drivers as small as possible and the drivens as big as possible. So, in theory, the finest feed you can get with the metric conversion set is 60,60,63 as drivens with 28,30,35 as drivers and a gear box setting of 56, which gives 0.002" which (just by coincidence I think) is the same as the finest feed from the imperial set up using the reversible threads/fine-feed gear. I hope this makes sense, cheers, Rod Edited By David Clark 1 on 04/09/2011 14:09:25
David Clark 1	04/09/2011 14:10:51
3357 forum posts 112 photos 10 articles	Hi John Anna was banned. Now reinstated. She posted a glamour photo and I thought we were headed for another husband wanted scenario. regards David
John Stevenson	04/09/2011 15:42:59
Moderator 5068 forum posts 3 photos	Repost the photo - sod the Myford.
JasonB	04/09/2011 16:40:53
Moderator 23374 forum posts 2825 photos 1 articles	"She posted a glamour photo and I thought we were headed for another husband wanted scenario." I thought that maybe you had answered Anna'a add for a husband and that was why you are selling up your workshop and house, then moving in with her and her Myford. Hope your recent Ill health has not forced the sale. J
_Paul_	04/09/2011 17:25:00
543 forum posts 31 photos	Posted by John Stevenson on 04/09/2011 15:42:59: Repost the photo - sod the Myford. ROFL
chris stephens	04/09/2011 18:40:11
1049 forum posts 1 photos	What John said, got to be better than some photos. chriStephens
Anna Jablonska	04/09/2011 19:57:53
14 forum posts 1 photos	Not quite sure why I should be banned Mr. Clark. This is my photo, and I'm proud of the way I look. If anyone feels it is inappropriate, please do let me know. Kindest regards Anna
Anna Jablonska	04/09/2011 20:00:14
14 forum posts 1 photos	Dear Rod et al., Thank you very much for taking the time to reply. I will read in detail what you have written, and if I may I will get back to you soon. Kindest Anna
John Stevenson	04/09/2011 20:37:42
Moderator 5068 forum posts 3 photos	Anna, Long post so go get a coffee. I used to have an ML7, bought new from Myfords and it served me well for many years. I always wanted a screwcutting gearbox but they were too expensive for me at the time. Years later I came across one quite reasonable so bought it and fitted it to my lathe. I wanted one to save the hassle of keep changing gears for the wide variety of jobs I was doing I then had to buy the new banjo and conversion gears from Myfords for doing metric threads, as there were no cheap rubber Indian copies I had to pay full price. After doing a few imperial threads then metric threads I realised I had made a big mistake in doing this conversion. Let me explain. When in imperial mode provided that the ration needed is in the box then there is no problem. You have quickly selectable ratios and a quickly selectable fine feed arrangement by just turning the gear over which requires no tools, after all this is what it was designed for in 1953 when metric was well into the future. The problem comes about when you swap to metric screwcutting. Instead of having to replace a few change wheels on a banjo yo now had to strip the original banjo, replace it with a new one and then populate this with the gears needed. Far, far more work than swapping gears on a non- gearbox lathe. Added to this you lost the fine feed arrangement when in metric mode and if needed entailed the whole job lot to be swapped over again. It was this constant swapping that made me realise that I had made a bad decision in fitting the gearbox. Shortly after this I sold the lathe as room was needed for a far larger lathe. In hindsight and knowing what I now know IF I still had the lathe I would keep the gearbox and the default original drive and purchase just two additional gears to enable the standard box to cut metric AND still have the default fine feed arrangement. The gearbox machines have a 24 tooth input gear on the tumbler shaft as standard. If this gear is replaced with a 33 tooth or 34 tooth, depending, then the standard box will cut all the common metric threads from 0.45 to 4.5mm pitch and BA sizes from 0 to 8 although a 20 and 21 is also needed for some of these sizes. It is far easier to replace one gear than swap a load or the whole banjo. Now if David will allow me a small plug these gears with a laminated chart can be bought here Metric Screwcutting Gears John S. Edited By John Stevenson on 04/09/2011 20:40:48
Anna Jablonska	04/09/2011 20:48:04
14 forum posts 1 photos	Dear John., Thank you very much for that informed response. As with Rod's, I'll mull it over a cup of coffee as you so rightly suggest, and get back to you as soon as I can. Kindest regards., Anna
John McNamara	05/09/2011 10:20:17
1341 forum posts 127 photos	Hi All Should I or should I not express a view on this? Well here goes……. There is a very basic tenet in British law, the presumption of innocence. And the possible guilt in this case was a presumption that a post by a female person on an engineering related site; created a prima facie case for the presumption of guilt, based on the reasoning that it is extremely unlikely that a female person would be interested in engineering. And therefore that person must have an ulterior motive. Let's look at the facts on this issue. Female Engineers are on the increase. Women are taking an increasing role in the sciences and that includes engineering, a couple of Google searches confirmed this. General Google search: Increase in Female Engineers....... More specifically in the UK...... As the second post above also suggests that in spite of their scholastic achievements they still face poor employment prospects; why? Because (some) of the broader Engineering community particularly the more senior or for want of a better word older men are still trapped in the mire of the past. Fortunately the world is evolving and times do change. It is also worth considering the perilous state of model engineering, we need every member we can get, Not just for the ME site but as members of the model engineering, I prefer to say Engineering community, it is in all our interests to recruit new members whenever we can. Cheers John
Ian P	05/09/2011 10:27:09
2597 forum posts 114 photos	I fully agree with John's reply (& John Stevensons too!) but whilst it is very nice of Anna to put her picture up, so Anna, please leave it there. As engineers though, what we really need to see is her workshop Ian P
David Clark 1	05/09/2011 11:49:27
3357 forum posts 112 photos 10 articles	Hi There A woman joined the Model Engineer website. She posted a glamour photo of herself. Not a problem. She was based in Poland. Alarm bells rang so I suspended her temporarily. I don't see a problem. regards David
DMB	05/09/2011 12:23:12
1399 forum posts 1 photos	How about if Anna shows us all what she`s got, in terms of a workshop, that is!
blowlamp	05/09/2011 12:34:54
1688 forum posts 106 photos	In my opinion, David's glamour shot is much more provocative. Martin.
JasonB	05/09/2011 13:52:05
Moderator 23374 forum posts 2825 photos 1 articles	I can see why david did it, there is a lot of similar spam about - eastern European ladies looking for husbands etc. I expect she was temporarily suspended while David confirmed Anna was a genuine member. Perfectly acceptable moderation in my view. Now Where is that Avitar of Diane's J
NJH	05/09/2011 14:47:14
2314 forum posts 139 photos	Hi Anna Welcome to the talking shop that is the ME forum - although at times Colosseum might be a more suitable name than Forum ! As far as David's categorisation of your Avitar as a "glamour" 'photo well I think he should get out more - it seems perfectly OK to me - but he IS the boss so we must accept his point. So to the point of your question - I'm very pleased that you asked it. I had been vaguely considering adding the metric conversion set to my S7 and I'm glad now that I did not. John S's answer is just the way to go for me so thanks to you both for this flash of insight! As far as having the woman's touch on this site I say welcome - please continue to contribute. It may be that it will encourage some better manners and more polite exchanges - but I wouldn't bet on it! Cheers Norman
Diane Carney	05/09/2011 19:36:37
Moderator 414 forum posts 11 photos	Jako jedyna kobieta na tym forum, że byłoby miło mieć jakieś firmy! Anna, wyślij zdjęcie kilku rzeczy, które dokonały lub modele robisz właśnie teraz. Następnie cynicy tutaj będzie wiedział, gdzie stoją. Diane ps JasonB - Diane don't do glam
NJH	05/09/2011 20:00:07
2314 forum posts 139 photos	Diane !!!!!!!!! That's quite out of order! Alright quite often I can't fully understand what my wife is on about but your post well........ Please translate so that we all may share the joke (?) Regards Norman