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screw slot width convention? (Read 2410 times)

CW Oldtimer Offline Posts: 534 Joined: Feb 20^th, 2018	screw slot width convention? Mar 17^th, 2021 at 1:03pm	Print Post
	This latest large snow storm gave me a chance to spend some time in the shop. Cleaning and putting away should have been the task. Instead I got distracted and made some screws for the low wall projects I have been trying to complete. Two screws needed are the machine screws that goes through the rear tang and the forearm screws. I made a few sets. I've often wondered how and why gun screws have the size slots they do. They don't seem to follow any pattern or convention. Some are so wide you can't find a blade thick enough to fit it correctly and then some screws are fitted with extremely thin slots. These later, if ever hard to get out can bend the thin blades required to fit them. I chanced learning something from the "iner-tube" (Google) whom I do not like to support in any way.... and looked for some kind of chart relating the size of slot to the standard blade width. There are numerous charts but nothing relating to what I wanted. ...No Luck! One way to learn more would be open dad's American Machinists' Handbook, 1940. But first, I thought it would be interesting to see what firearm specific info could be found among this group.
	« Last Edit: Mar 17^th, 2021 at 9:16pm by CW »

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GT Frequent Elocutionist Offline Posts: 2368 Location: Northeast Wyoming Joined: Jun 28^th, 2015	Re: screw slot width convention? Reply #1 - Mar 17^th, 2021 at 1:48pm	Print Post
	CW, Here is a chart taken from a 11th edition Machinery's Handbook (1941) I seem to reference frequently. My real determining factor in most cases is what slotting blades do I have at my disposal... most common that I have in my stash is a .031" wide, and I use that on most screws so that I can take an allen wrench that fits my mag bit screwdriver and make all my bits the same thickness just change their widths accordingly. The other part about screw slot widths is what is aesthetically pleasing to your eye? Functional or not, I personally find wide slots detract from the appearance of a firearm. My 2¢ Greg

	"To invent, you need a good imagination and a pile of junk" T. A. Edison "The trouble ain't that there is too many fools, but that the lightning ain't distributed right" M.T.
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bobw Frequent Elocutionist Offline Posts: 2109 Location: NW, Iowa Joined: Mar 19^th, 2013	Re: screw slot width convention? Reply #2 - Mar 17^th, 2021 at 6:25pm	Print Post
	I would agree with Greg. I like thin slots and usually use a .025 blade but they always seem to end up at .030. A none machinist (me) problem I would guess. Bob


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ssdave Frequent Elocutionist Offline Posts: 2138 Location: Eastern Oregon Joined: Apr 16^th, 2004	Re: screw slot width convention? Reply #3 - Mar 17^th, 2021 at 7:11pm	Print Post
	From the maintenance standpoint, slots are extremely irritating. I have every insert Brownells offered, and have their magnatip kit. I have every flat tip that Zephyr (maker of the highest quality bits in the US) makes. At one time, I went through their list and ordered 2 or 3 of every size. I have every tip made by MAC, in both metric and US sizes, I think that kit has 125 bits in it. I think they're Apex. I have a block that holds about 550 insert bits, and it's about 1/3 full of every random slotted bit I have ever run into. Last night I was taking sights off of a mid 70's model 70 and mounting a scope. Out of all the bits I had on hand, I did not have bits that perfectly fit the screws, and the sights took different bit for each set of screws. When I got bits the right thickness, they were too narrow or too wide. The only way I ever get a bit that fits correctly is to go to the mill or the grinder and cut one down to fit correctly. Really pity the fellow that tries working on guns with his 20 piece Craftsaman set, or even the nice 12 to 30 or so piece Chapman sets.


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John Boy Ex Member	Re: screw slot width convention? Reply #4 - Mar 17^th, 2021 at 7:34pm	Print Post
	I bought this set of computer bits to augment for the little screws (You need to *Login* or *Register* to view media files and links)


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CW Oldtimer Offline Posts: 534 Joined: Feb 20^th, 2018	Re: screw slot width convention? Reply #5 - Mar 18^th, 2021 at 11:17am	Print Post
	Thank you for the replies. The conformation that the standard is loose at best agrees with what we see in factory rifles. Greg, I like your answer or ideas. Plus I think there is general agreement that the narrow slots look best. Rifles with screws slots made to except coins, don't often fall into the "Fine Rifle" category. So, ...I'll just keep eyeballing it.


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Chuckster Frequent Elocutionist Online Posts: 2313 Location: Colorado Joined: May 15^th, 2008	Re: screw slot width convention? Reply #6 - Mar 18^th, 2021 at 10:55pm	Print Post
	Like narrow slots, but practical gets in the way. Ground a Woodruff cutter to cut a .040" slot. #6 through 1/4" all the same, different depths. Different width screwdrivers but same thickness. Chuck


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MrTipUp Frequent Elocutionist Offline Quality is to a product what character is to a man Posts: 1404 Location: Indiana Joined: Feb 19^th, 2020	Re: screw slot width convention? Reply #7 - Mar 19^th, 2021 at 9:47am	Print Post
	Am I the only one here who still uses slotting files? Of my three -1.1, 0.9. and 0.7 mm - the one I most often use is the 0.7 mm followed by the 0.9 mm. The 1.1 mm slot only looks right on the largest screw heads such as butt plate and tang screws; but even for those I sometimes use the 0.9 mm. And like others here, I sometimes have to grind a bit to the correct width. As for sets, my most-used set is a vintage Chapman, followed by a an original Magna-Tip, and then a whole mess of customized bits that fit one of my two handles. Lastly, I have found the mini ratchet wrench (which John Chapman invented and patented) a life- and screw-saver many times. Bill Lawrence


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marlinguy Frequent Elocutionist Offline Ballards may be weaker, but they sure are neater! Posts: 18067 Location: Oregon Joined: Feb 2^nd, 2009	Re: screw slot width convention? Reply #8 - Mar 19^th, 2021 at 10:47am	Print Post
	I use screw slot files to clean up slots, but not to cut them. I use my mill to cut slots in screws I've made. I made up an adapter for my tool rest to hold the flex shaft on my Dremel tool, and I clamp it to my tool rest. Then put my screw into the drill chuck fitted to the head on my mill. I use a thin disc to cut the slot in the screw head, and then if needed I use my slot files to clean it up. Takes some time to set it up, but I rarely build aa screw, and don't mind doing it for the rare occasion.

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GT Frequent Elocutionist Offline Posts: 2368 Location: Northeast Wyoming Joined: Jun 28^th, 2015	Re: screw slot width convention? Reply #9 - Mar 19^th, 2021 at 1:26pm	Print Post
	Bill, Call me lazy, when I can I use a machine to do these tasks Here's a couple finished this am for the Sharps I'm working on. Please note the high tech arbor for holding the slitting saw too. (a 5/16" allen cap screw with the end turned to 1/4" to fit in the collet) Greg

	"To invent, you need a good imagination and a pile of junk" T. A. Edison "The trouble ain't that there is too many fools, but that the lightning ain't distributed right" M.T.
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