jjr2001 (01-15-2017)
[QUOTE=olderdan;83420]Dan,Originally Posted by A bit of trigonometry is all that is required to calculate what those angles should be given the nose and clearance angles that we are after, and I made a spreadsheet to do the heavy lifting. [/B
I have no secrets so I am quite happy to make the spreadsheet available to the forum. I'll check it over first to check how easy it would be for dim wits to use intuitively. Maybe I need to write a short "how to use" file. It might be a few days because the lines bringing the landline which I use for the internet were torn down a couple of days ago by a wayward truck and I'm on a backup system at the moment which has the same speed as the old dialup connections. Who remembers those days? One of the problems of living out of town. Accordingly, I am unable to upload anything substantial at the moment.
In the morning I'll be looking into changing over to the WiMax system, because I am always having problems with my existing ADSL system. I'd be glad to hear from anyone who has had experience with WiMax.
Last edited by tonyfoale; 01-08-2017 at 12:55 PM.
jjr2001 (01-15-2017)
[QUOTE=olderdan;83420]Dan,Originally Posted by A bit of trigonometry is all that is required to calculate what those angles should be given the nose and clearance angles that we are after, and I made a spreadsheet to do the heavy lifting. [/B
I have uploaded the spreadsheet to https://motochassis.com/FileDump/Tan...g%20angles.xls
Also I suggest that everyone interested should download and read this excellent article on drill point geometry
DRILL POINT GEOMETRY by JOSEPH MAZOFF
Instructions;
Download to a folder of your choice. Open in excel.
There are two calculation pages and two matching graph pages, one pair for drill bits and the other for near flat end mills.
On each page there is only one data entry box, which is coloured green. DO NOT change any other values or you'll mess up the formulae.
1. Drill bit page.
Enter the included angle required for the bit, usually but not always 118 deg. Then look down the "relief angle" column until you find the nearest value to the 1st clearance angle that you want. For example say we want a clearance angle of 5 deg. we see values of 4.85 and 5.38. Now look across to the values of base angle and twist angle. The base angles are 31.31 and 31.39, and the twist angles are 9 and 10 deg. So we need to set the base angle to 31.3 deg and the twist angle to 9 or 10 deg.
You might ask why I didn't make the relief angle values in whole numbers so that we could go exactly to 5 deg. Well if I did that we would get a base angle of 31.33 deg and a twist angle of 9.29 deg. Do you see the problem now? The spindexer only indexes in whole degrees so 9.29 is not available. So if we set that to 9 deg. and the base angle to 31.3 then we get a clearance angle of 4.85 instead of our target of 5. I would not cry over that difference. Or you could choose 10 deg and get a clearance angle of 5.35 deg.
When you have ground the 1st clearance angles you repeat the lookup again for the 2nd clearance angle. Typically 20 to 25 deg. Let's go for 20, scroll down and we get 19.93 which corresponds to a base angle of 38.1 deg and a twist angle of 40 deg.
2. Endmill/slot drill page.
here in the green box we enter the 1st clearance angle, say 7 deg. Then look down to get the dish angle, typically 1 to 2 deg. We see that 2.05 deg is the nearest which requires the base angle of 7.3 deg and the twist (spindexer) angle of 107 deg.
In practice you will not have to look up these values each time because you'll be using the same values for many jobs. You'll mostly want to do all your drill bits to the same point and clearance angles so you only need to note down the settings for those.
I must point out that this spreadsheet is only valid for use with a 2 axes grinder as I have described in the main text. It has no validity for more traditional T&C grinders.
Don't hesitate to ask I haven't made anything clear. Here is an example screen shot.
Last edited by tonyfoale; 11-30-2018 at 02:38 AM. Reason: Text addition.
Thanks tonyfoale! We've added your Tool and Cutter Grinder to our Grinding category,
as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:
Thanks tonyfoale! We've added your Spin Indexer Modification to our Machining category,
as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:
tonyfoale (01-10-2017)
Thanks tonyfoale! We've added your Grinding Angle Spreadsheet to our Grinding category,
as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:
tonyfoale (01-10-2017)
Try unchecking the "Automatically parse links in text" and "Automatically retrieve titles from external links" options when posting; sometimes the forum url posting feature tries too hard to be clever.
We also have a new Practice Posting subforum where you can play around with the features.
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philipUsesWood&Brass (07-01-2018), tonyfoale (01-10-2017)
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